kernel26-magellan/patches-2.6.21-r13/0001-2.6.21-sd-0.48.patch

Staircase Deadline cpu scheduler policy
================================================

Design summary
==============

A novel design which incorporates a foreground-background descending priority
system (the staircase) via a bandwidth allocation matrix according to nice
level.


Features
========

A starvation free, strict fairness O(1) scalable design with interactivity
as good as the above restrictions can provide. There is no interactivity
estimator, no sleep/run measurements and only simple fixed accounting.
The design has strict enough a design and accounting that task behaviour
can be modelled and maximum scheduling latencies can be predicted by
the virtual deadline mechanism that manages runqueues. The prime concern
in this design is to maintain fairness at all costs determined by nice level,
yet to maintain as good interactivity as can be allowed within the
constraints of strict fairness.


Design description
==================

SD works off the principle of providing each task a quota of runtime that it is
allowed to run at a number of priority levels determined by its static priority
(ie. its nice level). If the task uses up its quota it has its priority
decremented to the next level determined by a priority matrix. Once every
runtime quota has been consumed of every priority level, a task is queued on the
"expired" array. When no other tasks exist with quota, the expired array is
activated and fresh quotas are handed out. This is all done in O(1).

Design details
==============

Each task keeps a record of its own entitlement of cpu time. Most of the rest of
these details apply to non-realtime tasks as rt task management is straight
forward.

Each runqueue keeps a record of what major epoch it is up to in the
rq->prio_rotation field which is incremented on each major epoch. It also
keeps a record of the current prio_level for each static priority task.

Each task keeps a record of what major runqueue epoch it was last running
on in p->rotation. It also keeps a record of what priority levels it has
already been allocated quota from during this epoch in a bitmap p->bitmap.

The only tunable that determines all other details is the RR_INTERVAL. This
is set to 8ms, and is scaled gently upwards with more cpus. This value is
tunable via a /proc interface.

All tasks are initially given a quota based on RR_INTERVAL. This is equal to
RR_INTERVAL between nice values of -6 and 0, half that size above nice 0, and
progressively larger for nice values from -1 to -20. This is assigned to
p->quota and only changes with changes in nice level.

As a task is first queued, it checks in recalc_task_prio to see if it has run at
this runqueue's current priority rotation. If it has not, it will have its
p->prio level set according to the first slot in a "priority matrix" and will be
given a p->time_slice equal to the p->quota, and has its allocation bitmap bit
set in p->bitmap for this prio level. It is then queued on the current active
priority array.

If a task has already been running during this major epoch, and it has
p->time_slice left and the rq->prio_quota for the task's p->prio still
has quota, it will be placed back on the active array, but no more quota
will be added.

If a task has been running during this major epoch, but does not have
p->time_slice left, it will find the next lowest priority in its bitmap that it
has not been allocated quota from. It then gets the a full quota in
p->time_slice. It is then queued on the current active priority array at the
newly determined lower priority.

If a task has been running during this major epoch, and does not have
any entitlement left in p->bitmap and no time_slice left, it will have its
bitmap cleared, and be queued at its best prio again, but on the expired
priority array.

When a task is queued, it has its relevant bit set in the array->prio_bitmap.

p->time_slice is stored in nanosconds and is updated via update_cpu_clock on
schedule() and scheduler_tick. If p->time_slice is below zero then the
recalc_task_prio is readjusted and the task rescheduled.


Priority Matrix
===============

In order to minimise the latencies between tasks of different nice levels
running concurrently, the dynamic priority slots where different nice levels
are queued are dithered instead of being sequential. What this means is that
there are 40 priority slots where a task may run during one major rotation,
and the allocation of slots is dependant on nice level. In the
following table, a zero represents a slot where the task may run.

PRIORITY:0..................20.................39
nice -20 0000000000000000000000000000000000000000
nice -10 1000100010001000100010001000100010010000
nice   0 1010101010101010101010101010101010101010
nice   5 1011010110110101101101011011010110110110
nice  10 1110111011101110111011101110111011101110
nice  15 1111111011111110111111101111111011111110
nice  19 1111111111111111111111111111111111111110

As can be seen, a nice -20 task runs in every priority slot whereas a nice 19
task only runs one slot per major rotation. This dithered table allows for the
smallest possible maximum latencies between tasks of varying nice levels, thus
allowing vastly different nice levels to be used.

SCHED_BATCH tasks are managed slightly differently, receiving only the top
slots from its priority bitmap giving it equal cpu as SCHED_NORMAL, but
slightly higher latencies.


Modelling deadline behaviour
============================

As the accounting in this design is hard and not modified by sleep average
calculations or interactivity modifiers, it is possible to accurately
predict the maximum latency that a task may experience under different
conditions. This is a virtual deadline mechanism enforced by mandatory
timeslice expiration and not outside bandwidth measurement.

The maximum duration a task can run during one major epoch is determined by its
nice value. Nice 0 tasks can run at 19 different priority levels for RR_INTERVAL
duration during each epoch. Nice 10 tasks can run at 9 priority levels for each
epoch, and so on. The table in the priority matrix above demonstrates how this
is enforced.

Therefore the maximum duration a runqueue epoch can take is determined by
the number of tasks running, and their nice level. After that, the maximum
duration it can take before a task can wait before it get scheduled is
determined by the position of its first slot on the matrix.

In the following examples, these are _worst case scenarios_ and would rarely
occur, but can be modelled nonetheless to determine the maximum possible
latency.

So for example, if two nice 0 tasks are running, and one has just expired as
another is activated for the first time receiving a full quota for this
runqueue rotation, the first task will wait:

nr_tasks * max_duration + nice_difference * rr_interval
1 * 19 * RR_INTERVAL + 0 = 152ms

In the presence of a nice 10 task, a nice 0 task would wait a maximum of
1 * 10 * RR_INTERVAL + 0 = 80ms

In the presence of a nice 0 task, a nice 10 task would wait a maximum of
1 * 19 * RR_INTERVAL + 1 * RR_INTERVAL = 160ms

More useful than these values, though, are the average latencies which are
a matter of determining the average distance between priority slots of
different nice values and multiplying them by the tasks' quota. For example
in the presence of a nice -10 task, a nice 0 task will wait either one or
two slots. Given that nice -10 tasks have a quota 2.5 times the RR_INTERVAL,
this means the latencies will alternate between 2.5 and 5 RR_INTERVALs or
20 and 40ms respectively (on uniprocessor at 1000HZ).


Achieving interactivity
=======================

A requirement of this scheduler design was to achieve good interactivity
despite being a completely fair deadline based design. The disadvantage of
designs that try to achieve interactivity is that they usually do so at
the expense of maintaining fairness. As cpu speeds increase, the requirement
for some sort of metered unfairness towards interactive tasks becomes a less
desirable phenomenon, but low latency and fairness remains mandatory to
good interactive performance.

This design relies on the fact that interactive tasks, by their nature,
sleep often. Most fair scheduling designs end up penalising such tasks
indirectly giving them less than their fair possible share because of the
sleep, and have to use a mechanism of bonusing their priority to offset
this based on the duration they sleep. This becomes increasingly inaccurate
as the number of running tasks rises and more tasks spend time waiting on
runqueues rather than sleeping, and it is impossible to tell whether the
task that's waiting on a runqueue only intends to run for a short period and
then sleep again after than runqueue wait. Furthermore, all such designs rely
on a period of time to pass to accumulate some form of statistic on the task
before deciding on how much to give them preference. The shorter this period,
the more rapidly bursts of cpu ruin the interactive tasks behaviour. The
longer this period, the longer it takes for interactive tasks to get low
scheduling latencies and fair cpu.

This design does not measure sleep time at all. Interactive tasks that sleep
often will wake up having consumed very little if any of their quota for
the current major priority rotation. The longer they have slept, the less
likely they are to even be on the current major priority rotation. Once
woken up, though, they get to use up a their full quota for that epoch,
whether part of a quota remains or a full quota. Overall, however, they
can still only run as much cpu time for that epoch as any other task of the
same nice level. This means that two tasks behaving completely differently
from fully cpu bound to waking/sleeping extremely frequently will still
get the same quota of cpu, but the latter will be using its quota for that
epoch in bursts rather than continuously. This guarantees that interactive
tasks get the same amount of cpu as cpu bound ones.

The other requirement of interactive tasks is also to obtain low latencies
for when they are scheduled. Unlike fully cpu bound tasks and the maximum
latencies possible described in the modelling deadline behaviour section
above, tasks that sleep will wake up with quota available usually at the
current runqueue's priority_level or better. This means that the most latency
they are likely to see is one RR_INTERVAL, and often they will preempt the
current task if it is not of a sleeping nature. This then guarantees very
low latency for interactive tasks, and the lowest latencies for the least
cpu bound tasks.


Fri, 4 May 2007

Signed-off-by: Con Kolivas <kernel@kolivas.org>

---
 Documentation/sched-design.txt  |  234 +++++++
 Documentation/sysctl/kernel.txt |   14 
 fs/pipe.c                       |    7 
 fs/proc/array.c                 |    2 
 include/linux/init_task.h       |    4 
 include/linux/sched.h           |   32 -
 kernel/sched.c                  | 1277 +++++++++++++++++++---------------------
 kernel/softirq.c                |    2 
 kernel/sysctl.c                 |   26 
 kernel/workqueue.c              |    2 
 10 files changed, 908 insertions(+), 692 deletions(-)

Index: linux-2.6.21-ck2/kernel/workqueue.c
===================================================================
--- linux-2.6.21-ck2.orig/kernel/workqueue.c	2007-05-03 22:20:57.000000000 +1000
+++ linux-2.6.21-ck2/kernel/workqueue.c	2007-05-14 19:30:30.000000000 +1000
@@ -355,8 +355,6 @@ static int worker_thread(void *__cwq)
 	if (!cwq->freezeable)
 		current->flags |= PF_NOFREEZE;
 
-	set_user_nice(current, -5);
-
 	/* Block and flush all signals */
 	sigfillset(&blocked);
 	sigprocmask(SIG_BLOCK, &blocked, NULL);
Index: linux-2.6.21-ck2/fs/proc/array.c
===================================================================
--- linux-2.6.21-ck2.orig/fs/proc/array.c	2007-05-03 22:20:56.000000000 +1000
+++ linux-2.6.21-ck2/fs/proc/array.c	2007-05-14 19:30:30.000000000 +1000
@@ -165,7 +165,6 @@ static inline char * task_state(struct t
 	rcu_read_lock();
 	buffer += sprintf(buffer,
 		"State:\t%s\n"
-		"SleepAVG:\t%lu%%\n"
 		"Tgid:\t%d\n"
 		"Pid:\t%d\n"
 		"PPid:\t%d\n"
@@ -173,7 +172,6 @@ static inline char * task_state(struct t
 		"Uid:\t%d\t%d\t%d\t%d\n"
 		"Gid:\t%d\t%d\t%d\t%d\n",
 		get_task_state(p),
-		(p->sleep_avg/1024)*100/(1020000000/1024),
 	       	p->tgid, p->pid,
 	       	pid_alive(p) ? rcu_dereference(p->real_parent)->tgid : 0,
 		pid_alive(p) && p->ptrace ? rcu_dereference(p->parent)->pid : 0,
Index: linux-2.6.21-ck2/include/linux/init_task.h
===================================================================
--- linux-2.6.21-ck2.orig/include/linux/init_task.h	2007-05-03 22:20:57.000000000 +1000
+++ linux-2.6.21-ck2/include/linux/init_task.h	2007-05-14 19:30:30.000000000 +1000
@@ -102,13 +102,15 @@ extern struct group_info init_groups;
 	.prio		= MAX_PRIO-20,					\
 	.static_prio	= MAX_PRIO-20,					\
 	.normal_prio	= MAX_PRIO-20,					\
+	.rotation	= 0,						\
 	.policy		= SCHED_NORMAL,					\
 	.cpus_allowed	= CPU_MASK_ALL,					\
 	.mm		= NULL,						\
 	.active_mm	= &init_mm,					\
 	.run_list	= LIST_HEAD_INIT(tsk.run_list),			\
 	.ioprio		= 0,						\
-	.time_slice	= HZ,						\
+	.time_slice	= 1000000000,						\
+	.quota		= 1000000000,						\
 	.tasks		= LIST_HEAD_INIT(tsk.tasks),			\
 	.ptrace_children= LIST_HEAD_INIT(tsk.ptrace_children),		\
 	.ptrace_list	= LIST_HEAD_INIT(tsk.ptrace_list),		\
Index: linux-2.6.21-ck2/include/linux/sched.h
===================================================================
--- linux-2.6.21-ck2.orig/include/linux/sched.h	2007-05-03 22:20:57.000000000 +1000
+++ linux-2.6.21-ck2/include/linux/sched.h	2007-05-14 19:30:30.000000000 +1000
@@ -149,8 +149,7 @@ extern unsigned long weighted_cpuload(co
 #define EXIT_ZOMBIE		16
 #define EXIT_DEAD		32
 /* in tsk->state again */
-#define TASK_NONINTERACTIVE	64
-#define TASK_DEAD		128
+#define TASK_DEAD		64
 
 #define __set_task_state(tsk, state_value)		\
 	do { (tsk)->state = (state_value); } while (0)
@@ -522,8 +521,9 @@ struct signal_struct {
 
 #define MAX_USER_RT_PRIO	100
 #define MAX_RT_PRIO		MAX_USER_RT_PRIO
+#define PRIO_RANGE		(40)
 
-#define MAX_PRIO		(MAX_RT_PRIO + 40)
+#define MAX_PRIO		(MAX_RT_PRIO + PRIO_RANGE)
 
 #define rt_prio(prio)		unlikely((prio) < MAX_RT_PRIO)
 #define rt_task(p)		rt_prio((p)->prio)
@@ -788,13 +788,6 @@ struct mempolicy;
 struct pipe_inode_info;
 struct uts_namespace;
 
-enum sleep_type {
-	SLEEP_NORMAL,
-	SLEEP_NONINTERACTIVE,
-	SLEEP_INTERACTIVE,
-	SLEEP_INTERRUPTED,
-};
-
 struct prio_array;
 
 struct task_struct {
@@ -814,20 +807,33 @@ struct task_struct {
 	int load_weight;	/* for niceness load balancing purposes */
 	int prio, static_prio, normal_prio;
 	struct list_head run_list;
+	/*
+	 * This bitmap shows what priorities this task has received quota
+	 * from for this major priority rotation on its current runqueue.
+	 */
+	DECLARE_BITMAP(bitmap, PRIO_RANGE + 1);
 	struct prio_array *array;
+	/* Which major runqueue rotation did this task run */
+	unsigned long rotation;
 
 	unsigned short ioprio;
 #ifdef CONFIG_BLK_DEV_IO_TRACE
 	unsigned int btrace_seq;
 #endif
-	unsigned long sleep_avg;
 	unsigned long long timestamp, last_ran;
 	unsigned long long sched_time; /* sched_clock time spent running */
-	enum sleep_type sleep_type;
 
 	unsigned long policy;
 	cpumask_t cpus_allowed;
-	unsigned int time_slice, first_time_slice;
+	/*
+	 * How much this task is entitled to run at the current priority
+	 * before being requeued at a lower priority.
+	 */
+	int time_slice;
+	/* Is this the very first time_slice this task has ever run. */
+	unsigned int first_time_slice;
+	/* How much this task receives at each priority level */
+	int quota;
 
 #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
 	struct sched_info sched_info;
Index: linux-2.6.21-ck2/kernel/sched.c
===================================================================
--- linux-2.6.21-ck2.orig/kernel/sched.c	2007-05-03 22:20:57.000000000 +1000
+++ linux-2.6.21-ck2/kernel/sched.c	2007-05-14 19:30:30.000000000 +1000
@@ -16,6 +16,7 @@
  *		by Davide Libenzi, preemptible kernel bits by Robert Love.
  *  2003-09-03	Interactivity tuning by Con Kolivas.
  *  2004-04-02	Scheduler domains code by Nick Piggin
+ *  2007-03-02	Staircase deadline scheduling policy by Con Kolivas
  */
 
 #include <linux/mm.h>
@@ -52,6 +53,7 @@
 #include <linux/tsacct_kern.h>
 #include <linux/kprobes.h>
 #include <linux/delayacct.h>
+#include <linux/log2.h>
 #include <asm/tlb.h>
 
 #include <asm/unistd.h>
@@ -83,126 +85,72 @@ unsigned long long __attribute__((weak))
 #define USER_PRIO(p)		((p)-MAX_RT_PRIO)
 #define TASK_USER_PRIO(p)	USER_PRIO((p)->static_prio)
 #define MAX_USER_PRIO		(USER_PRIO(MAX_PRIO))
+#define SCHED_PRIO(p)		((p)+MAX_RT_PRIO)
 
-/*
- * Some helpers for converting nanosecond timing to jiffy resolution
- */
-#define NS_TO_JIFFIES(TIME)	((TIME) / (1000000000 / HZ))
+/* Some helpers for converting to/from various scales.*/
 #define JIFFIES_TO_NS(TIME)	((TIME) * (1000000000 / HZ))
-
-/*
- * These are the 'tuning knobs' of the scheduler:
- *
- * Minimum timeslice is 5 msecs (or 1 jiffy, whichever is larger),
- * default timeslice is 100 msecs, maximum timeslice is 800 msecs.
- * Timeslices get refilled after they expire.
- */
-#define MIN_TIMESLICE		max(5 * HZ / 1000, 1)
-#define DEF_TIMESLICE		(100 * HZ / 1000)
-#define ON_RUNQUEUE_WEIGHT	 30
-#define CHILD_PENALTY		 95
-#define PARENT_PENALTY		100
-#define EXIT_WEIGHT		  3
-#define PRIO_BONUS_RATIO	 25
-#define MAX_BONUS		(MAX_USER_PRIO * PRIO_BONUS_RATIO / 100)
-#define INTERACTIVE_DELTA	  2
-#define MAX_SLEEP_AVG		(DEF_TIMESLICE * MAX_BONUS)
-#define STARVATION_LIMIT	(MAX_SLEEP_AVG)
-#define NS_MAX_SLEEP_AVG	(JIFFIES_TO_NS(MAX_SLEEP_AVG))
-
-/*
- * If a task is 'interactive' then we reinsert it in the active
- * array after it has expired its current timeslice. (it will not
- * continue to run immediately, it will still roundrobin with
- * other interactive tasks.)
- *
- * This part scales the interactivity limit depending on niceness.
- *
- * We scale it linearly, offset by the INTERACTIVE_DELTA delta.
- * Here are a few examples of different nice levels:
- *
- *  TASK_INTERACTIVE(-20): [1,1,1,1,1,1,1,1,1,0,0]
- *  TASK_INTERACTIVE(-10): [1,1,1,1,1,1,1,0,0,0,0]
- *  TASK_INTERACTIVE(  0): [1,1,1,1,0,0,0,0,0,0,0]
- *  TASK_INTERACTIVE( 10): [1,1,0,0,0,0,0,0,0,0,0]
- *  TASK_INTERACTIVE( 19): [0,0,0,0,0,0,0,0,0,0,0]
- *
- * (the X axis represents the possible -5 ... 0 ... +5 dynamic
- *  priority range a task can explore, a value of '1' means the
- *  task is rated interactive.)
- *
- * Ie. nice +19 tasks can never get 'interactive' enough to be
- * reinserted into the active array. And only heavily CPU-hog nice -20
- * tasks will be expired. Default nice 0 tasks are somewhere between,
- * it takes some effort for them to get interactive, but it's not
- * too hard.
- */
-
-#define CURRENT_BONUS(p) \
-	(NS_TO_JIFFIES((p)->sleep_avg) * MAX_BONUS / \
-		MAX_SLEEP_AVG)
-
-#define GRANULARITY	(10 * HZ / 1000 ? : 1)
-
-#ifdef CONFIG_SMP
-#define TIMESLICE_GRANULARITY(p)	(GRANULARITY * \
-		(1 << (((MAX_BONUS - CURRENT_BONUS(p)) ? : 1) - 1)) * \
-			num_online_cpus())
-#else
-#define TIMESLICE_GRANULARITY(p)	(GRANULARITY * \
-		(1 << (((MAX_BONUS - CURRENT_BONUS(p)) ? : 1) - 1)))
-#endif
-
-#define SCALE(v1,v1_max,v2_max) \
-	(v1) * (v2_max) / (v1_max)
-
-#define DELTA(p) \
-	(SCALE(TASK_NICE(p) + 20, 40, MAX_BONUS) - 20 * MAX_BONUS / 40 + \
-		INTERACTIVE_DELTA)
-
-#define TASK_INTERACTIVE(p) \
-	((p)->prio <= (p)->static_prio - DELTA(p))
-
-#define INTERACTIVE_SLEEP(p) \
-	(JIFFIES_TO_NS(MAX_SLEEP_AVG * \
-		(MAX_BONUS / 2 + DELTA((p)) + 1) / MAX_BONUS - 1))
-
-#define TASK_PREEMPTS_CURR(p, rq) \
-	((p)->prio < (rq)->curr->prio)
-
-#define SCALE_PRIO(x, prio) \
-	max(x * (MAX_PRIO - prio) / (MAX_USER_PRIO / 2), MIN_TIMESLICE)
-
-static unsigned int static_prio_timeslice(int static_prio)
-{
-	if (static_prio < NICE_TO_PRIO(0))
-		return SCALE_PRIO(DEF_TIMESLICE * 4, static_prio);
-	else
-		return SCALE_PRIO(DEF_TIMESLICE, static_prio);
-}
-
-/*
- * task_timeslice() scales user-nice values [ -20 ... 0 ... 19 ]
- * to time slice values: [800ms ... 100ms ... 5ms]
- *
- * The higher a thread's priority, the bigger timeslices
- * it gets during one round of execution. But even the lowest
- * priority thread gets MIN_TIMESLICE worth of execution time.
+#define MS_TO_NS(TIME)		((TIME) * 1000000)
+#define MS_TO_US(TIME)		((TIME) * 1000)
+#define US_TO_MS(TIME)		((TIME) / 1000)
+
+#define TASK_PREEMPTS_CURR(p, curr)	((p)->prio < (curr)->prio)
+
+/*
+ * This is the time all tasks within the same priority round robin.
+ * Value is in ms and set to a minimum of 8ms. Scales with number of cpus.
+ * Tunable via /proc interface.
+ */
+int rr_interval __read_mostly = 8;
+
+/*
+ * This contains a bitmap for each dynamic priority level with empty slots
+ * for the valid priorities each different nice level can have. It allows
+ * us to stagger the slots where differing priorities run in a way that
+ * keeps latency differences between different nice levels at a minimum.
+ * The purpose of a pre-generated matrix is for rapid lookup of next slot in
+ * O(1) time without having to recalculate every time priority gets demoted.
+ * All nice levels use priority slot 39 as this allows less niced tasks to
+ * get all priority slots better than that before expiration is forced.
+ * ie, where 0 means a slot for that priority, priority running from left to
+ * right is from prio 0 to prio 39:
+ * nice -20 0000000000000000000000000000000000000000
+ * nice -10 1000100010001000100010001000100010010000
+ * nice   0 1010101010101010101010101010101010101010
+ * nice   5 1011010110110101101101011011010110110110
+ * nice  10 1110111011101110111011101110111011101110
+ * nice  15 1111111011111110111111101111111011111110
+ * nice  19 1111111111111111111111111111111111111110
  */
+static unsigned long prio_matrix[PRIO_RANGE][BITS_TO_LONGS(PRIO_RANGE)]
+				 __read_mostly;
 
-static inline unsigned int task_timeslice(struct task_struct *p)
-{
-	return static_prio_timeslice(p->static_prio);
-}
+struct rq;
 
 /*
  * These are the runqueue data structures:
  */
-
 struct prio_array {
-	unsigned int nr_active;
-	DECLARE_BITMAP(bitmap, MAX_PRIO+1); /* include 1 bit for delimiter */
+	/* Tasks queued at each priority */
 	struct list_head queue[MAX_PRIO];
+
+	/*
+	 * The bitmap of priorities queued for this array. While the expired
+	 * array will never have realtime tasks on it, it is simpler to have
+	 * equal sized bitmaps for a cheap array swap. Include 1 bit for
+	 * delimiter.
+	 */
+	DECLARE_BITMAP(prio_bitmap, MAX_PRIO + 1);
+
+	/*
+	 * The best static priority (of the dynamic priority tasks) queued
+	 * this array.
+	 */
+	int best_static_prio;
+
+#ifdef CONFIG_SMP
+	/* For convenience looks back at rq */
+	struct rq *rq;
+#endif
 };
 
 /*
@@ -234,14 +182,24 @@ struct rq {
 	 */
 	unsigned long nr_uninterruptible;
 
-	unsigned long expired_timestamp;
 	/* Cached timestamp set by update_cpu_clock() */
 	unsigned long long most_recent_timestamp;
 	struct task_struct *curr, *idle;
 	unsigned long next_balance;
 	struct mm_struct *prev_mm;
+
 	struct prio_array *active, *expired, arrays[2];
-	int best_expired_prio;
+	unsigned long *dyn_bitmap, *exp_bitmap;
+
+	/*
+	 * The current dynamic priority level this runqueue is at per static
+	 * priority level.
+	 */
+	int prio_level[PRIO_RANGE];
+
+	/* How many times we have rotated the priority queue */
+	unsigned long prio_rotation;
+
 	atomic_t nr_iowait;
 
 #ifdef CONFIG_SMP
@@ -579,12 +537,9 @@ static inline struct rq *this_rq_lock(vo
 #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
 /*
  * Called when a process is dequeued from the active array and given
- * the cpu.  We should note that with the exception of interactive
- * tasks, the expired queue will become the active queue after the active
- * queue is empty, without explicitly dequeuing and requeuing tasks in the
- * expired queue.  (Interactive tasks may be requeued directly to the
- * active queue, thus delaying tasks in the expired queue from running;
- * see scheduler_tick()).
+ * the cpu.  We should note that the expired queue will become the active
+ * queue after the active queue is empty, without explicitly dequeuing and
+ * requeuing tasks in the expired queue.
  *
  * This function is only called from sched_info_arrive(), rather than
  * dequeue_task(). Even though a task may be queued and dequeued multiple
@@ -682,71 +637,227 @@ sched_info_switch(struct task_struct *pr
 #define sched_info_switch(t, next)	do { } while (0)
 #endif /* CONFIG_SCHEDSTATS || CONFIG_TASK_DELAY_ACCT */
 
+static inline int task_queued(struct task_struct *task)
+{
+	return !list_empty(&task->run_list);
+}
+
+static inline void set_dynamic_bit(struct task_struct *p, struct rq *rq)
+{
+	__set_bit(p->prio, p->array->prio_bitmap);
+}
+
 /*
- * Adding/removing a task to/from a priority array:
+ * Removing from a runqueue.
  */
-static void dequeue_task(struct task_struct *p, struct prio_array *array)
+static void dequeue_task(struct task_struct *p, struct rq *rq)
 {
-	array->nr_active--;
-	list_del(&p->run_list);
-	if (list_empty(array->queue + p->prio))
-		__clear_bit(p->prio, array->bitmap);
+	list_del_init(&p->run_list);
+	if (list_empty(p->array->queue + p->prio))
+		__clear_bit(p->prio, p->array->prio_bitmap);
 }
 
-static void enqueue_task(struct task_struct *p, struct prio_array *array)
+static void reset_first_time_slice(struct task_struct *p)
 {
-	sched_info_queued(p);
-	list_add_tail(&p->run_list, array->queue + p->prio);
-	__set_bit(p->prio, array->bitmap);
-	array->nr_active++;
+	if (unlikely(p->first_time_slice))
+		p->first_time_slice = 0;
+}
+
+/*
+ * The task is being queued on a fresh array so it has its entitlement
+ * bitmap cleared.
+ */
+static void task_new_array(struct task_struct *p, struct rq *rq,
+			   struct prio_array *array)
+{
+	bitmap_zero(p->bitmap, PRIO_RANGE);
+	p->rotation = rq->prio_rotation;
+	p->time_slice = p->quota;
 	p->array = array;
+	reset_first_time_slice(p);
+}
+
+/* Find the first slot from the relevant prio_matrix entry */
+static int first_prio_slot(struct task_struct *p)
+{
+	if (unlikely(p->policy == SCHED_BATCH))
+		return p->static_prio;
+	return SCHED_PRIO(find_first_zero_bit(
+		prio_matrix[USER_PRIO(p->static_prio)], PRIO_RANGE));
 }
 
 /*
- * Put task to the end of the run list without the overhead of dequeue
- * followed by enqueue.
+ * Find the first unused slot by this task that is also in its prio_matrix
+ * level. SCHED_BATCH tasks do not use the priority matrix. They only take
+ * priority slots from their static_prio and above.
  */
-static void requeue_task(struct task_struct *p, struct prio_array *array)
+static int next_entitled_slot(struct task_struct *p, struct rq *rq)
 {
-	list_move_tail(&p->run_list, array->queue + p->prio);
+	int search_prio = MAX_RT_PRIO, uprio = USER_PRIO(p->static_prio);
+	struct prio_array *array = rq->active;
+	DECLARE_BITMAP(tmp, PRIO_RANGE);
+
+	/*
+	 * Go straight to expiration if there are higher priority tasks
+	 * already expired.
+	 */
+	if (p->static_prio > rq->expired->best_static_prio)
+		return MAX_PRIO;
+	if (!rq->prio_level[uprio])
+		rq->prio_level[uprio] = MAX_RT_PRIO;
+	/*
+	 * Only priorities equal to the prio_level and above for their
+	 * static_prio are acceptable, and only if it's not better than
+	 * a queued better static_prio's prio_level.
+	 */
+	if (p->static_prio < array->best_static_prio) {
+		if (likely(p->policy != SCHED_BATCH))
+			array->best_static_prio = p->static_prio;
+	} else if (p->static_prio == array->best_static_prio) {
+		search_prio = rq->prio_level[uprio];
+	} else {
+		int i;
+
+		search_prio = rq->prio_level[uprio];
+		/* A bound O(n) function, worst case n is 40 */
+		for (i = array->best_static_prio; i <= p->static_prio ; i++) {
+			if (!rq->prio_level[USER_PRIO(i)])
+				rq->prio_level[USER_PRIO(i)] = MAX_RT_PRIO;
+			search_prio = max(search_prio,
+				      rq->prio_level[USER_PRIO(i)]);
+		}
+	}
+	if (unlikely(p->policy == SCHED_BATCH)) {
+		search_prio = max(search_prio, p->static_prio);
+		return SCHED_PRIO(find_next_zero_bit(p->bitmap, PRIO_RANGE,
+				  USER_PRIO(search_prio)));
+	}
+	bitmap_or(tmp, p->bitmap, prio_matrix[uprio], PRIO_RANGE);
+	return SCHED_PRIO(find_next_zero_bit(tmp, PRIO_RANGE,
+		USER_PRIO(search_prio)));
+}
+
+static void queue_expired(struct task_struct *p, struct rq *rq)
+{
+	task_new_array(p, rq, rq->expired);
+	p->prio = p->normal_prio = first_prio_slot(p);
+	if (p->static_prio < rq->expired->best_static_prio)
+		rq->expired->best_static_prio = p->static_prio;
+	reset_first_time_slice(p);
 }
 
-static inline void
-enqueue_task_head(struct task_struct *p, struct prio_array *array)
+#ifdef CONFIG_SMP
+/*
+ * If we're waking up a task that was previously on a different runqueue,
+ * update its data appropriately. Note we may be reading data from src_rq->
+ * outside of lock, but the occasional inaccurate result should be harmless.
+ */
+ static void update_if_moved(struct task_struct *p, struct rq *rq)
+{
+	struct rq *src_rq = p->array->rq;
+
+	if (src_rq == rq)
+		return;
+	/*
+	 * Only need to set p->array when p->rotation == rq->prio_rotation as
+	 * they will be set in recalc_task_prio when != rq->prio_rotation.
+	 */
+	if (p->rotation == src_rq->prio_rotation) {
+		p->rotation = rq->prio_rotation;
+		if (p->array == src_rq->expired)
+			p->array = rq->expired;
+		else
+			p->array = rq->active;
+	} else
+		p->rotation = 0;
+}
+#else
+static inline void update_if_moved(struct task_struct *p, struct rq *rq)
 {
-	list_add(&p->run_list, array->queue + p->prio);
-	__set_bit(p->prio, array->bitmap);
-	array->nr_active++;
-	p->array = array;
 }
+#endif
 
 /*
- * __normal_prio - return the priority that is based on the static
- * priority but is modified by bonuses/penalties.
- *
- * We scale the actual sleep average [0 .... MAX_SLEEP_AVG]
- * into the -5 ... 0 ... +5 bonus/penalty range.
- *
- * We use 25% of the full 0...39 priority range so that:
- *
- * 1) nice +19 interactive tasks do not preempt nice 0 CPU hogs.
- * 2) nice -20 CPU hogs do not get preempted by nice 0 tasks.
- *
- * Both properties are important to certain workloads.
+ * recalc_task_prio determines what priority a non rt_task will be
+ * queued at. If the task has already been running during this runqueue's
+ * major rotation (rq->prio_rotation) then it continues at the same
+ * priority if it has tick entitlement left. If it does not have entitlement
+ * left, it finds the next priority slot according to its nice value that it
+ * has not extracted quota from. If it has not run during this major
+ * rotation, it starts at the next_entitled_slot and has its bitmap quota
+ * cleared. If it does not have any slots left it has all its slots reset and
+ * is queued on the expired at its first_prio_slot.
  */
+static void recalc_task_prio(struct task_struct *p, struct rq *rq)
+{
+	struct prio_array *array = rq->active;
+	int queue_prio;
 
-static inline int __normal_prio(struct task_struct *p)
+	update_if_moved(p, rq);
+	if (p->rotation == rq->prio_rotation) {
+		if (p->array == array) {
+			if (p->time_slice > 0)
+				return;
+			p->time_slice = p->quota;
+		} else if (p->array == rq->expired) {
+			queue_expired(p, rq);
+			return;
+		} else
+			task_new_array(p, rq, array);
+	} else
+		task_new_array(p, rq, array);
+
+	queue_prio = next_entitled_slot(p, rq);
+	if (queue_prio >= MAX_PRIO) {
+		queue_expired(p, rq);
+		return;
+	}
+	p->prio = p->normal_prio = queue_prio;
+	__set_bit(USER_PRIO(p->prio), p->bitmap);
+}
+
+/*
+ * Adding to a runqueue. The dynamic priority queue that it is added to is
+ * determined by recalc_task_prio() above.
+ */
+static inline void __enqueue_task(struct task_struct *p, struct rq *rq)
+{
+	if (rt_task(p))
+		p->array = rq->active;
+	else
+		recalc_task_prio(p, rq);
+
+	sched_info_queued(p);
+	set_dynamic_bit(p, rq);
+}
+
+static void enqueue_task(struct task_struct *p, struct rq *rq)
 {
-	int bonus, prio;
+	__enqueue_task(p, rq);
+	list_add_tail(&p->run_list, p->array->queue + p->prio);
+}
 
-	bonus = CURRENT_BONUS(p) - MAX_BONUS / 2;
+static inline void enqueue_task_head(struct task_struct *p, struct rq *rq)
+{
+	__enqueue_task(p, rq);
+	list_add(&p->run_list, p->array->queue + p->prio);
+}
 
-	prio = p->static_prio - bonus;
-	if (prio < MAX_RT_PRIO)
-		prio = MAX_RT_PRIO;
-	if (prio > MAX_PRIO-1)
-		prio = MAX_PRIO-1;
-	return prio;
+/*
+ * requeue_task is only called when p->static_prio does not change. p->prio
+ * can change with dynamic tasks.
+ */
+static void requeue_task(struct task_struct *p, struct rq *rq,
+			 struct prio_array *old_array, int old_prio)
+{
+	if (p->array == rq->expired)
+		queue_expired(p, rq);
+	list_move_tail(&p->run_list, p->array->queue + p->prio);
+	if (!rt_task(p)) {
+		if (list_empty(old_array->queue + old_prio))
+			__clear_bit(old_prio, old_array->prio_bitmap);
+		set_dynamic_bit(p, rq);
+	}
 }
 
 /*
@@ -759,17 +870,24 @@ static inline int __normal_prio(struct t
  */
 
 /*
- * Assume: static_prio_timeslice(NICE_TO_PRIO(0)) == DEF_TIMESLICE
- * If static_prio_timeslice() is ever changed to break this assumption then
- * this code will need modification
- */
-#define TIME_SLICE_NICE_ZERO DEF_TIMESLICE
-#define LOAD_WEIGHT(lp) \
-	(((lp) * SCHED_LOAD_SCALE) / TIME_SLICE_NICE_ZERO)
-#define PRIO_TO_LOAD_WEIGHT(prio) \
-	LOAD_WEIGHT(static_prio_timeslice(prio))
-#define RTPRIO_TO_LOAD_WEIGHT(rp) \
-	(PRIO_TO_LOAD_WEIGHT(MAX_RT_PRIO) + LOAD_WEIGHT(rp))
+ * task_timeslice - the total duration a task can run during one major
+ * rotation. Returns value in milliseconds as the smallest value can be 1.
+ */
+static int task_timeslice(struct task_struct *p)
+{
+	int slice = p->quota;	/* quota is in us */
+
+	if (!rt_task(p))
+		slice += (PRIO_RANGE - 1 - TASK_USER_PRIO(p)) * slice;
+	return US_TO_MS(slice);
+}
+
+/*
+ * The load weight is basically the task_timeslice in ms. Realtime tasks are
+ * special cased to be proportionately larger than nice -20 by their
+ * rt_priority. The weight for rt tasks can only be arbitrary at best.
+ */
+#define RTPRIO_TO_LOAD_WEIGHT(rp)	(rr_interval * 20 * (40 + rp))
 
 static void set_load_weight(struct task_struct *p)
 {
@@ -786,7 +904,7 @@ static void set_load_weight(struct task_
 #endif
 			p->load_weight = RTPRIO_TO_LOAD_WEIGHT(p->rt_priority);
 	} else
-		p->load_weight = PRIO_TO_LOAD_WEIGHT(p->static_prio);
+		p->load_weight = task_timeslice(p);
 }
 
 static inline void
@@ -814,28 +932,38 @@ static inline void dec_nr_running(struct
 }
 
 /*
- * Calculate the expected normal priority: i.e. priority
- * without taking RT-inheritance into account. Might be
- * boosted by interactivity modifiers. Changes upon fork,
- * setprio syscalls, and whenever the interactivity
- * estimator recalculates.
+ * __activate_task - move a task to the runqueue.
  */
-static inline int normal_prio(struct task_struct *p)
+static inline void __activate_task(struct task_struct *p, struct rq *rq)
+{
+	enqueue_task(p, rq);
+	inc_nr_running(p, rq);
+}
+
+/*
+ * __activate_idle_task - move idle task to the _front_ of runqueue.
+ */
+static inline void __activate_idle_task(struct task_struct *p, struct rq *rq)
 {
-	int prio;
+	enqueue_task_head(p, rq);
+	inc_nr_running(p, rq);
+}
 
+static inline int normal_prio(struct task_struct *p)
+{
 	if (has_rt_policy(p))
-		prio = MAX_RT_PRIO-1 - p->rt_priority;
+		return MAX_RT_PRIO-1 - p->rt_priority;
+	/* Other tasks all have normal_prio set in recalc_task_prio */
+	if (likely(p->prio >= MAX_RT_PRIO && p->prio < MAX_PRIO))
+		return p->prio;
 	else
-		prio = __normal_prio(p);
-	return prio;
+		return p->static_prio;
 }
 
 /*
  * Calculate the current priority, i.e. the priority
  * taken into account by the scheduler. This value might
- * be boosted by RT tasks, or might be boosted by
- * interactivity modifiers. Will be RT if the task got
+ * be boosted by RT tasks as it will be RT if the task got
  * RT-boosted. If not then it returns p->normal_prio.
  */
 static int effective_prio(struct task_struct *p)
@@ -852,111 +980,41 @@ static int effective_prio(struct task_st
 }
 
 /*
- * __activate_task - move a task to the runqueue.
+ * All tasks have quotas based on rr_interval. RT tasks all get rr_interval.
+ * From nice 1 to 19 they are smaller than it only if they are at least one
+ * tick still. Below nice 0 they get progressively larger.
+ * ie nice -6..0 = rr_interval. nice -10 = 2.5 * rr_interval
+ * nice -20 = 10 * rr_interval. nice 1-19 = rr_interval / 2.
+ * Value returned is in microseconds.
  */
-static void __activate_task(struct task_struct *p, struct rq *rq)
+static inline unsigned int rr_quota(struct task_struct *p)
 {
-	struct prio_array *target = rq->active;
-
-	if (batch_task(p))
-		target = rq->expired;
-	enqueue_task(p, target);
-	inc_nr_running(p, rq);
-}
+	int nice = TASK_NICE(p), rr = rr_interval;
 
-/*
- * __activate_idle_task - move idle task to the _front_ of runqueue.
- */
-static inline void __activate_idle_task(struct task_struct *p, struct rq *rq)
-{
-	enqueue_task_head(p, rq->active);
-	inc_nr_running(p, rq);
+	if (!rt_task(p)) {
+		if (nice < -6) {
+			rr *= nice * nice;
+			rr /= 40;
+		} else if (nice > 0)
+			rr = rr / 2 ? : 1;
+	}
+	return MS_TO_US(rr);
 }
 
-/*
- * Recalculate p->normal_prio and p->prio after having slept,
- * updating the sleep-average too:
- */
-static int recalc_task_prio(struct task_struct *p, unsigned long long now)
+/* Every time we set the quota we need to set the load weight */
+static void set_quota(struct task_struct *p)
 {
-	/* Caller must always ensure 'now >= p->timestamp' */
-	unsigned long sleep_time = now - p->timestamp;
-
-	if (batch_task(p))
-		sleep_time = 0;
-
-	if (likely(sleep_time > 0)) {
-		/*
-		 * This ceiling is set to the lowest priority that would allow
-		 * a task to be reinserted into the active array on timeslice
-		 * completion.
-		 */
-		unsigned long ceiling = INTERACTIVE_SLEEP(p);
-
-		if (p->mm && sleep_time > ceiling && p->sleep_avg < ceiling) {
-			/*
-			 * Prevents user tasks from achieving best priority
-			 * with one single large enough sleep.
-			 */
-			p->sleep_avg = ceiling;
-			/*
-			 * Using INTERACTIVE_SLEEP() as a ceiling places a
-			 * nice(0) task 1ms sleep away from promotion, and
-			 * gives it 700ms to round-robin with no chance of
-			 * being demoted.  This is more than generous, so
-			 * mark this sleep as non-interactive to prevent the
-			 * on-runqueue bonus logic from intervening should
-			 * this task not receive cpu immediately.
-			 */
-			p->sleep_type = SLEEP_NONINTERACTIVE;
-		} else {
-			/*
-			 * Tasks waking from uninterruptible sleep are
-			 * limited in their sleep_avg rise as they
-			 * are likely to be waiting on I/O
-			 */
-			if (p->sleep_type == SLEEP_NONINTERACTIVE && p->mm) {
-				if (p->sleep_avg >= ceiling)
-					sleep_time = 0;
-				else if (p->sleep_avg + sleep_time >=
-					 ceiling) {
-						p->sleep_avg = ceiling;
-						sleep_time = 0;
-				}
-			}
-
-			/*
-			 * This code gives a bonus to interactive tasks.
-			 *
-			 * The boost works by updating the 'average sleep time'
-			 * value here, based on ->timestamp. The more time a
-			 * task spends sleeping, the higher the average gets -
-			 * and the higher the priority boost gets as well.
-			 */
-			p->sleep_avg += sleep_time;
-
-		}
-		if (p->sleep_avg > NS_MAX_SLEEP_AVG)
-			p->sleep_avg = NS_MAX_SLEEP_AVG;
-	}
-
-	return effective_prio(p);
+	p->quota = rr_quota(p);
+	set_load_weight(p);
 }
 
 /*
  * activate_task - move a task to the runqueue and do priority recalculation
- *
- * Update all the scheduling statistics stuff. (sleep average
- * calculation, priority modifiers, etc.)
  */
 static void activate_task(struct task_struct *p, struct rq *rq, int local)
 {
-	unsigned long long now;
-
-	if (rt_task(p))
-		goto out;
+	unsigned long long now = sched_clock();
 
-	now = sched_clock();
 #ifdef CONFIG_SMP
 	if (!local) {
 		/* Compensate for drifting sched_clock */
@@ -977,32 +1035,9 @@ static void activate_task(struct task_st
 				     (now - p->timestamp) >> 20);
 	}
 
-	p->prio = recalc_task_prio(p, now);
-
-	/*
-	 * This checks to make sure it's not an uninterruptible task
-	 * that is now waking up.
-	 */
-	if (p->sleep_type == SLEEP_NORMAL) {
-		/*
-		 * Tasks which were woken up by interrupts (ie. hw events)
-		 * are most likely of interactive nature. So we give them
-		 * the credit of extending their sleep time to the period
-		 * of time they spend on the runqueue, waiting for execution
-		 * on a CPU, first time around:
-		 */
-		if (in_interrupt())
-			p->sleep_type = SLEEP_INTERRUPTED;
-		else {
-			/*
-			 * Normal first-time wakeups get a credit too for
-			 * on-runqueue time, but it will be weighted down:
-			 */
-			p->sleep_type = SLEEP_INTERACTIVE;
-		}
-	}
+	set_quota(p);
+	p->prio = effective_prio(p);
 	p->timestamp = now;
-out:
 	__activate_task(p, rq);
 }
 
@@ -1012,8 +1047,7 @@ out:
 static void deactivate_task(struct task_struct *p, struct rq *rq)
 {
 	dec_nr_running(p, rq);
-	dequeue_task(p, p->array);
-	p->array = NULL;
+	dequeue_task(p, rq);
 }
 
 /*
@@ -1095,7 +1129,7 @@ migrate_task(struct task_struct *p, int 
 	 * If the task is not on a runqueue (and not running), then
 	 * it is sufficient to simply update the task's cpu field.
 	 */
-	if (!p->array && !task_running(rq, p)) {
+	if (!task_queued(p) && !task_running(rq, p)) {
 		set_task_cpu(p, dest_cpu);
 		return 0;
 	}
@@ -1126,7 +1160,7 @@ void wait_task_inactive(struct task_stru
 repeat:
 	rq = task_rq_lock(p, &flags);
 	/* Must be off runqueue entirely, not preempted. */
-	if (unlikely(p->array || task_running(rq, p))) {
+	if (unlikely(task_queued(p) || task_running(rq, p))) {
 		/* If it's preempted, we yield.  It could be a while. */
 		preempted = !task_running(rq, p);
 		task_rq_unlock(rq, &flags);
@@ -1391,6 +1425,31 @@ static inline int wake_idle(int cpu, str
 }
 #endif
 
+/*
+ * We need to have a special definition for an idle runqueue when testing
+ * for preemption on CONFIG_HOTPLUG_CPU as the idle task may be scheduled as
+ * a realtime task in sched_idle_next.
+ */
+#ifdef CONFIG_HOTPLUG_CPU
+#define rq_idle(rq)	((rq)->curr == (rq)->idle && !rt_task((rq)->curr))
+#else
+#define rq_idle(rq)	((rq)->curr == (rq)->idle)
+#endif
+
+static inline int task_preempts_curr(struct task_struct *p, struct rq *rq)
+{
+	struct task_struct *curr = rq->curr;
+
+	return ((p->array == task_rq(p)->active &&
+		TASK_PREEMPTS_CURR(p, curr)) || rq_idle(rq));
+}
+
+static inline void try_preempt(struct task_struct *p, struct rq *rq)
+{
+	if (task_preempts_curr(p, rq))
+		resched_task(rq->curr);
+}
+
 /***
  * try_to_wake_up - wake up a thread
  * @p: the to-be-woken-up thread
@@ -1422,7 +1481,7 @@ static int try_to_wake_up(struct task_st
 	if (!(old_state & state))
 		goto out;
 
-	if (p->array)
+	if (task_queued(p))
 		goto out_running;
 
 	cpu = task_cpu(p);
@@ -1515,7 +1574,7 @@ out_set_cpu:
 		old_state = p->state;
 		if (!(old_state & state))
 			goto out;
-		if (p->array)
+		if (task_queued(p))
 			goto out_running;
 
 		this_cpu = smp_processor_id();
@@ -1524,25 +1583,9 @@ out_set_cpu:
 
 out_activate:
 #endif /* CONFIG_SMP */
-	if (old_state == TASK_UNINTERRUPTIBLE) {
+	if (old_state == TASK_UNINTERRUPTIBLE)
 		rq->nr_uninterruptible--;
-		/*
-		 * Tasks on involuntary sleep don't earn
-		 * sleep_avg beyond just interactive state.
-		 */
-		p->sleep_type = SLEEP_NONINTERACTIVE;
-	} else
-
-	/*
-	 * Tasks that have marked their sleep as noninteractive get
-	 * woken up with their sleep average not weighted in an
-	 * interactive way.
-	 */
-		if (old_state & TASK_NONINTERACTIVE)
-			p->sleep_type = SLEEP_NONINTERACTIVE;
-
 
-	activate_task(p, rq, cpu == this_cpu);
 	/*
 	 * Sync wakeups (i.e. those types of wakeups where the waker
 	 * has indicated that it will leave the CPU in short order)
@@ -1551,10 +1594,9 @@ out_activate:
 	 * the waker guarantees that the freshly woken up task is going
 	 * to be considered on this CPU.)
 	 */
-	if (!sync || cpu != this_cpu) {
-		if (TASK_PREEMPTS_CURR(p, rq))
-			resched_task(rq->curr);
-	}
+	activate_task(p, rq, cpu == this_cpu);
+	if (!sync || cpu != this_cpu)
+		try_preempt(p, rq);
 	success = 1;
 
 out_running:
@@ -1577,7 +1619,6 @@ int fastcall wake_up_state(struct task_s
 	return try_to_wake_up(p, state, 0);
 }
 
-static void task_running_tick(struct rq *rq, struct task_struct *p);
 /*
  * Perform scheduler related setup for a newly forked process p.
  * p is forked by current.
@@ -1605,7 +1646,6 @@ void fastcall sched_fork(struct task_str
 	p->prio = current->normal_prio;
 
 	INIT_LIST_HEAD(&p->run_list);
-	p->array = NULL;
 #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
 	if (unlikely(sched_info_on()))
 		memset(&p->sched_info, 0, sizeof(p->sched_info));
@@ -1617,30 +1657,31 @@ void fastcall sched_fork(struct task_str
 	/* Want to start with kernel preemption disabled. */
 	task_thread_info(p)->preempt_count = 1;
 #endif
+	if (unlikely(p->policy == SCHED_FIFO))
+		goto out;
 	/*
 	 * Share the timeslice between parent and child, thus the
 	 * total amount of pending timeslices in the system doesn't change,
 	 * resulting in more scheduling fairness.
 	 */
 	local_irq_disable();
-	p->time_slice = (current->time_slice + 1) >> 1;
-	/*
-	 * The remainder of the first timeslice might be recovered by
-	 * the parent if the child exits early enough.
-	 */
-	p->first_time_slice = 1;
-	current->time_slice >>= 1;
-	p->timestamp = sched_clock();
-	if (unlikely(!current->time_slice)) {
+	if (current->time_slice > 0) {
+		current->time_slice /= 2;
+		if (current->time_slice)
+			p->time_slice = current->time_slice;
+		else
+			p->time_slice = 1;
 		/*
-		 * This case is rare, it happens when the parent has only
-		 * a single jiffy left from its timeslice. Taking the
-		 * runqueue lock is not a problem.
+		 * The remainder of the first timeslice might be recovered by
+		 * the parent if the child exits early enough.
 		 */
-		current->time_slice = 1;
-		task_running_tick(cpu_rq(cpu), current);
-	}
+		p->first_time_slice = 1;
+	} else
+		p->time_slice = 0;
+
+	p->timestamp = sched_clock();
 	local_irq_enable();
+out:
 	put_cpu();
 }
 
@@ -1662,38 +1703,16 @@ void fastcall wake_up_new_task(struct ta
 	this_cpu = smp_processor_id();
 	cpu = task_cpu(p);
 
-	/*
-	 * We decrease the sleep average of forking parents
-	 * and children as well, to keep max-interactive tasks
-	 * from forking tasks that are max-interactive. The parent
-	 * (current) is done further down, under its lock.
-	 */
-	p->sleep_avg = JIFFIES_TO_NS(CURRENT_BONUS(p) *
-		CHILD_PENALTY / 100 * MAX_SLEEP_AVG / MAX_BONUS);
-
-	p->prio = effective_prio(p);
-
 	if (likely(cpu == this_cpu)) {
+		activate_task(p, rq, 1);
 		if (!(clone_flags & CLONE_VM)) {
 			/*
 			 * The VM isn't cloned, so we're in a good position to
 			 * do child-runs-first in anticipation of an exec. This
 			 * usually avoids a lot of COW overhead.
 			 */
-			if (unlikely(!current->array))
-				__activate_task(p, rq);
-			else {
-				p->prio = current->prio;
-				p->normal_prio = current->normal_prio;
-				list_add_tail(&p->run_list, &current->run_list);
-				p->array = current->array;
-				p->array->nr_active++;
-				inc_nr_running(p, rq);
-			}
 			set_need_resched();
-		} else
-			/* Run child last */
-			__activate_task(p, rq);
+		}
 		/*
 		 * We skip the following code due to cpu == this_cpu
 	 	 *
@@ -1710,19 +1729,16 @@ void fastcall wake_up_new_task(struct ta
 		 */
 		p->timestamp = (p->timestamp - this_rq->most_recent_timestamp)
 					+ rq->most_recent_timestamp;
-		__activate_task(p, rq);
-		if (TASK_PREEMPTS_CURR(p, rq))
-			resched_task(rq->curr);
+		activate_task(p, rq, 0);
+		try_preempt(p, rq);
 
 		/*
 		 * Parent and child are on different CPUs, now get the
-		 * parent runqueue to update the parent's ->sleep_avg:
+		 * parent runqueue to update the parent's ->flags:
 		 */
 		task_rq_unlock(rq, &flags);
 		this_rq = task_rq_lock(current, &flags);
 	}
-	current->sleep_avg = JIFFIES_TO_NS(CURRENT_BONUS(current) *
-		PARENT_PENALTY / 100 * MAX_SLEEP_AVG / MAX_BONUS);
 	task_rq_unlock(this_rq, &flags);
 }
 
@@ -1737,23 +1753,17 @@ void fastcall wake_up_new_task(struct ta
  */
 void fastcall sched_exit(struct task_struct *p)
 {
+	struct task_struct *parent;
 	unsigned long flags;
 	struct rq *rq;
 
-	/*
-	 * If the child was a (relative-) CPU hog then decrease
-	 * the sleep_avg of the parent as well.
-	 */
-	rq = task_rq_lock(p->parent, &flags);
-	if (p->first_time_slice && task_cpu(p) == task_cpu(p->parent)) {
-		p->parent->time_slice += p->time_slice;
-		if (unlikely(p->parent->time_slice > task_timeslice(p)))
-			p->parent->time_slice = task_timeslice(p);
-	}
-	if (p->sleep_avg < p->parent->sleep_avg)
-		p->parent->sleep_avg = p->parent->sleep_avg /
-		(EXIT_WEIGHT + 1) * EXIT_WEIGHT + p->sleep_avg /
-		(EXIT_WEIGHT + 1);
+	parent = p->parent;
+	rq = task_rq_lock(parent, &flags);
+	if (p->first_time_slice > 0 && task_cpu(p) == task_cpu(parent)) {
+		parent->time_slice += p->time_slice;
+		if (unlikely(parent->time_slice > parent->quota))
+			parent->time_slice = parent->quota;
+	}
 	task_rq_unlock(rq, &flags);
 }
 
@@ -2085,23 +2095,17 @@ void sched_exec(void)
  * pull_task - move a task from a remote runqueue to the local runqueue.
  * Both runqueues must be locked.
  */
-static void pull_task(struct rq *src_rq, struct prio_array *src_array,
-		      struct task_struct *p, struct rq *this_rq,
-		      struct prio_array *this_array, int this_cpu)
+static void pull_task(struct rq *src_rq, struct task_struct *p,
+		      struct rq *this_rq, int this_cpu)
 {
-	dequeue_task(p, src_array);
+	dequeue_task(p, src_rq);
 	dec_nr_running(p, src_rq);
 	set_task_cpu(p, this_cpu);
 	inc_nr_running(p, this_rq);
-	enqueue_task(p, this_array);
+	enqueue_task(p, this_rq);
 	p->timestamp = (p->timestamp - src_rq->most_recent_timestamp)
 				+ this_rq->most_recent_timestamp;
-	/*
-	 * Note that idle threads have a prio of MAX_PRIO, for this test
-	 * to be always true for them.
-	 */
-	if (TASK_PREEMPTS_CURR(p, this_rq))
-		resched_task(this_rq->curr);
+	try_preempt(p, this_rq);
 }
 
 /*
@@ -2144,7 +2148,16 @@ int can_migrate_task(struct task_struct 
 	return 1;
 }
 
-#define rq_best_prio(rq) min((rq)->curr->prio, (rq)->best_expired_prio)
+static inline int rq_best_prio(struct rq *rq)
+{
+	int best_prio, exp_prio;
+
+	best_prio = sched_find_first_bit(rq->dyn_bitmap);
+	exp_prio = find_next_bit(rq->exp_bitmap, MAX_PRIO, MAX_RT_PRIO);
+	if (unlikely(best_prio > exp_prio))
+		best_prio = exp_prio;
+	return best_prio;
+}
 
 /*
  * move_tasks tries to move up to max_nr_move tasks and max_load_move weighted
@@ -2160,7 +2173,7 @@ static int move_tasks(struct rq *this_rq
 {
 	int idx, pulled = 0, pinned = 0, this_best_prio, best_prio,
 	    best_prio_seen, skip_for_load;
-	struct prio_array *array, *dst_array;
+	struct prio_array *array;
 	struct list_head *head, *curr;
 	struct task_struct *tmp;
 	long rem_load_move;
@@ -2187,26 +2200,21 @@ static int move_tasks(struct rq *this_rq
 	 * be cache-cold, thus switching CPUs has the least effect
 	 * on them.
 	 */
-	if (busiest->expired->nr_active) {
-		array = busiest->expired;
-		dst_array = this_rq->expired;
-	} else {
-		array = busiest->active;
-		dst_array = this_rq->active;
-	}
-
+	array = busiest->expired;
 new_array:
-	/* Start searching at priority 0: */
-	idx = 0;
+	/* Expired arrays don't have RT tasks so they're always MAX_RT_PRIO+ */
+	if (array == busiest->expired)
+		idx = MAX_RT_PRIO;
+	else
+		idx = 0;
 skip_bitmap:
 	if (!idx)
-		idx = sched_find_first_bit(array->bitmap);
+		idx = sched_find_first_bit(array->prio_bitmap);
 	else
-		idx = find_next_bit(array->bitmap, MAX_PRIO, idx);
+		idx = find_next_bit(array->prio_bitmap, MAX_PRIO, idx);
 	if (idx >= MAX_PRIO) {
-		if (array == busiest->expired && busiest->active->nr_active) {
+		if (array == busiest->expired) {
 			array = busiest->active;
-			dst_array = this_rq->active;
 			goto new_array;
 		}
 		goto out;
@@ -2237,7 +2245,7 @@ skip_queue:
 		goto skip_bitmap;
 	}
 
-	pull_task(busiest, array, tmp, this_rq, dst_array, this_cpu);
+	pull_task(busiest, tmp, this_rq, this_cpu);
 	pulled++;
 	rem_load_move -= tmp->load_weight;
 
@@ -3013,11 +3021,36 @@ EXPORT_PER_CPU_SYMBOL(kstat);
 /*
  * This is called on clock ticks and on context switches.
  * Bank in p->sched_time the ns elapsed since the last tick or switch.
+ * CPU scheduler quota accounting is also performed here in microseconds.
+ * The value returned from sched_clock() occasionally gives bogus values so
+ * some sanity checking is required.
  */
-static inline void
-update_cpu_clock(struct task_struct *p, struct rq *rq, unsigned long long now)
+static void
+update_cpu_clock(struct task_struct *p, struct rq *rq, unsigned long long now,
+		 int tick)
 {
-	p->sched_time += now - p->last_ran;
+	long time_diff = now - p->last_ran;
+
+	if (tick) {
+		/*
+		 * Called from scheduler_tick() there should be less than two
+		 * jiffies worth, and not negative/overflow.
+		 */
+		if (time_diff > JIFFIES_TO_NS(2) || time_diff < 0)
+			time_diff = JIFFIES_TO_NS(1);
+	} else {
+		/*
+		 * Called from context_switch there should be less than one
+		 * jiffy worth, and not negative/overflow. There should be
+		 * some time banked here so use a nominal 1us.
+		 */
+		if (time_diff > JIFFIES_TO_NS(1) || time_diff < 1)
+			time_diff = 1000;
+	}
+	/* time_slice accounting is done in usecs to avoid overflow on 32bit */
+	if (p != rq->idle && p->policy != SCHED_FIFO)
+		p->time_slice -= time_diff / 1000;
+	p->sched_time += time_diff;
 	p->last_ran = rq->most_recent_timestamp = now;
 }
 
@@ -3038,27 +3071,6 @@ unsigned long long current_sched_time(co
 }
 
 /*
- * We place interactive tasks back into the active array, if possible.
- *
- * To guarantee that this does not starve expired tasks we ignore the
- * interactivity of a task if the first expired task had to wait more
- * than a 'reasonable' amount of time. This deadline timeout is
- * load-dependent, as the frequency of array switched decreases with
- * increasing number of running tasks. We also ignore the interactivity
- * if a better static_prio task has expired:
- */
-static inline int expired_starving(struct rq *rq)
-{
-	if (rq->curr->static_prio > rq->best_expired_prio)
-		return 1;
-	if (!STARVATION_LIMIT || !rq->expired_timestamp)
-		return 0;
-	if (jiffies - rq->expired_timestamp > STARVATION_LIMIT * rq->nr_running)
-		return 1;
-	return 0;
-}
-
-/*
  * Account user cpu time to a process.
  * @p: the process that the cpu time gets accounted to
  * @hardirq_offset: the offset to subtract from hardirq_count()
@@ -3131,87 +3143,47 @@ void account_steal_time(struct task_stru
 		cpustat->steal = cputime64_add(cpustat->steal, tmp);
 }
 
-static void task_running_tick(struct rq *rq, struct task_struct *p)
+/*
+ * The task has used up its quota of running in this prio_level so it must be
+ * dropped a priority level, all managed by recalc_task_prio().
+ */
+static void task_expired_entitlement(struct rq *rq, struct task_struct *p)
 {
-	if (p->array != rq->active) {
-		/* Task has expired but was not scheduled yet */
-		set_tsk_need_resched(p);
+	int overrun;
+
+	reset_first_time_slice(p);
+	if (rt_task(p)) {
+		p->time_slice += p->quota;
+		list_move_tail(&p->run_list, p->array->queue + p->prio);
 		return;
 	}
-	spin_lock(&rq->lock);
+	overrun = p->time_slice;
+	dequeue_task(p, rq);
+	enqueue_task(p, rq);
 	/*
-	 * The task was running during this tick - update the
-	 * time slice counter. Note: we do not update a thread's
-	 * priority until it either goes to sleep or uses up its
-	 * timeslice. This makes it possible for interactive tasks
-	 * to use up their timeslices at their highest priority levels.
+	 * Subtract any extra time this task ran over its time_slice; ie
+	 * overrun will either be 0 or negative.
 	 */
-	if (rt_task(p)) {
-		/*
-		 * RR tasks need a special form of timeslice management.
-		 * FIFO tasks have no timeslices.
-		 */
-		if ((p->policy == SCHED_RR) && !--p->time_slice) {
-			p->time_slice = task_timeslice(p);
-			p->first_time_slice = 0;
-			set_tsk_need_resched(p);
-
-			/* put it at the end of the queue: */
-			requeue_task(p, rq->active);
-		}
-		goto out_unlock;
-	}
-	if (!--p->time_slice) {
-		dequeue_task(p, rq->active);
-		set_tsk_need_resched(p);
-		p->prio = effective_prio(p);
-		p->time_slice = task_timeslice(p);
-		p->first_time_slice = 0;
-
-		if (!rq->expired_timestamp)
-			rq->expired_timestamp = jiffies;
-		if (!TASK_INTERACTIVE(p) || expired_starving(rq)) {
-			enqueue_task(p, rq->expired);
-			if (p->static_prio < rq->best_expired_prio)
-				rq->best_expired_prio = p->static_prio;
-		} else
-			enqueue_task(p, rq->active);
-	} else {
-		/*
-		 * Prevent a too long timeslice allowing a task to monopolize
-		 * the CPU. We do this by splitting up the timeslice into
-		 * smaller pieces.
-		 *
-		 * Note: this does not mean the task's timeslices expire or
-		 * get lost in any way, they just might be preempted by
-		 * another task of equal priority. (one with higher
-		 * priority would have preempted this task already.) We
-		 * requeue this task to the end of the list on this priority
-		 * level, which is in essence a round-robin of tasks with
-		 * equal priority.
-		 *
-		 * This only applies to tasks in the interactive
-		 * delta range with at least TIMESLICE_GRANULARITY to requeue.
-		 */
-		if (TASK_INTERACTIVE(p) && !((task_timeslice(p) -
-			p->time_slice) % TIMESLICE_GRANULARITY(p)) &&
-			(p->time_slice >= TIMESLICE_GRANULARITY(p)) &&
-			(p->array == rq->active)) {
+	p->time_slice += overrun;
+}
 
-			requeue_task(p, rq->active);
-			set_tsk_need_resched(p);
-		}
-	}
-out_unlock:
+/* This manages tasks that have run out of timeslice during a scheduler_tick */
+static void task_running_tick(struct rq *rq, struct task_struct *p)
+{
+	/* SCHED_FIFO tasks never run out of timeslice. */
+	if (p->time_slice > 0 || p->policy == SCHED_FIFO)
+		return;
+	/* p->time_slice <= 0 */
+	spin_lock(&rq->lock);
+	if (likely(task_queued(p)))
+		task_expired_entitlement(rq, p);
+	set_tsk_need_resched(p);
 	spin_unlock(&rq->lock);
 }
 
 /*
  * This function gets called by the timer code, with HZ frequency.
  * We call it with interrupts disabled.
- *
- * It also gets called by the fork code, when changing the parent's
- * timeslices.
  */
 void scheduler_tick(void)
 {
@@ -3220,7 +3192,7 @@ void scheduler_tick(void)
 	int cpu = smp_processor_id();
 	struct rq *rq = cpu_rq(cpu);
 
-	update_cpu_clock(p, rq, now);
+	update_cpu_clock(p, rq, now, 1);
 
 	if (p != rq->idle)
 		task_running_tick(rq, p);
@@ -3269,10 +3241,55 @@ EXPORT_SYMBOL(sub_preempt_count);
 
 #endif
 
-static inline int interactive_sleep(enum sleep_type sleep_type)
+static void reset_prio_levels(struct rq *rq)
 {
-	return (sleep_type == SLEEP_INTERACTIVE ||
-		sleep_type == SLEEP_INTERRUPTED);
+	rq->active->best_static_prio = MAX_PRIO - 1;
+	rq->expired->best_static_prio = MAX_PRIO - 1;
+	memset(rq->prio_level, 0, sizeof(int) * PRIO_RANGE);
+}
+
+/*
+ * next_dynamic_task finds the next suitable dynamic task.
+ */
+static inline struct task_struct *next_dynamic_task(struct rq *rq, int idx)
+{
+	struct prio_array *array = rq->active;
+	struct task_struct *next;
+	struct list_head *queue;
+	int nstatic;
+
+retry:
+	if (idx >= MAX_PRIO) {
+		/* There are no more tasks in the active array. Swap arrays */
+		array = rq->expired;
+		rq->expired = rq->active;
+		rq->active = array;
+		rq->exp_bitmap = rq->expired->prio_bitmap;
+		rq->dyn_bitmap = rq->active->prio_bitmap;
+		rq->prio_rotation++;
+		idx = find_next_bit(rq->dyn_bitmap, MAX_PRIO, MAX_RT_PRIO);
+		reset_prio_levels(rq);
+	}
+	queue = array->queue + idx;
+	next = list_entry(queue->next, struct task_struct, run_list);
+	if (unlikely(next->time_slice <= 0)) {
+		/*
+		 * Unlucky enough that this task ran out of time_slice
+		 * before it hit a scheduler_tick so it should have its
+		 * priority reassessed and choose another task (possibly
+		 * the same one)
+		 */
+		task_expired_entitlement(rq, next);
+		idx = find_next_bit(rq->dyn_bitmap, MAX_PRIO, MAX_RT_PRIO);
+		goto retry;
+	}
+	next->rotation = rq->prio_rotation;
+	nstatic = next->static_prio;
+	if (nstatic < array->best_static_prio)
+		array->best_static_prio = nstatic;
+	if (idx > rq->prio_level[USER_PRIO(nstatic)])
+		rq->prio_level[USER_PRIO(nstatic)] = idx;
+	return next;
 }
 
 /*
@@ -3281,13 +3298,11 @@ static inline int interactive_sleep(enum
 asmlinkage void __sched schedule(void)
 {
 	struct task_struct *prev, *next;
-	struct prio_array *array;
 	struct list_head *queue;
 	unsigned long long now;
-	unsigned long run_time;
-	int cpu, idx, new_prio;
 	long *switch_count;
 	struct rq *rq;
+	int cpu, idx;
 
 	/*
 	 * Test if we are atomic.  Since do_exit() needs to call into
@@ -3323,18 +3338,6 @@ need_resched_nonpreemptible:
 
 	schedstat_inc(rq, sched_cnt);
 	now = sched_clock();
-	if (likely((long long)(now - prev->timestamp) < NS_MAX_SLEEP_AVG)) {
-		run_time = now - prev->timestamp;
-		if (unlikely((long long)(now - prev->timestamp) < 0))
-			run_time = 0;
-	} else
-		run_time = NS_MAX_SLEEP_AVG;
-
-	/*
-	 * Tasks charged proportionately less run_time at high sleep_avg to
-	 * delay them losing their interactive status
-	 */
-	run_time /= (CURRENT_BONUS(prev) ? : 1);
 
 	spin_lock_irq(&rq->lock);
 
@@ -3356,59 +3359,29 @@ need_resched_nonpreemptible:
 		idle_balance(cpu, rq);
 		if (!rq->nr_running) {
 			next = rq->idle;
-			rq->expired_timestamp = 0;
 			goto switch_tasks;
 		}
 	}
 
-	array = rq->active;
-	if (unlikely(!array->nr_active)) {
-		/*
-		 * Switch the active and expired arrays.
-		 */
-		schedstat_inc(rq, sched_switch);
-		rq->active = rq->expired;
-		rq->expired = array;
-		array = rq->active;
-		rq->expired_timestamp = 0;
-		rq->best_expired_prio = MAX_PRIO;
-	}
-
-	idx = sched_find_first_bit(array->bitmap);
-	queue = array->queue + idx;
-	next = list_entry(queue->next, struct task_struct, run_list);
-
-	if (!rt_task(next) && interactive_sleep(next->sleep_type)) {
-		unsigned long long delta = now - next->timestamp;
-		if (unlikely((long long)(now - next->timestamp) < 0))
-			delta = 0;
-
-		if (next->sleep_type == SLEEP_INTERACTIVE)
-			delta = delta * (ON_RUNQUEUE_WEIGHT * 128 / 100) / 128;
-
-		array = next->array;
-		new_prio = recalc_task_prio(next, next->timestamp + delta);
-
-		if (unlikely(next->prio != new_prio)) {
-			dequeue_task(next, array);
-			next->prio = new_prio;
-			enqueue_task(next, array);
-		}
+	idx = sched_find_first_bit(rq->dyn_bitmap);
+	if (!rt_prio(idx))
+		next = next_dynamic_task(rq, idx);
+	else {
+		queue = rq->active->queue + idx;
+		next = list_entry(queue->next, struct task_struct, run_list);
 	}
-	next->sleep_type = SLEEP_NORMAL;
 switch_tasks:
-	if (next == rq->idle)
+	if (next == rq->idle) {
+		reset_prio_levels(rq);
+		rq->prio_rotation++;
 		schedstat_inc(rq, sched_goidle);
+	}
 	prefetch(next);
 	prefetch_stack(next);
 	clear_tsk_need_resched(prev);
 	rcu_qsctr_inc(task_cpu(prev));
 
-	update_cpu_clock(prev, rq, now);
-
-	prev->sleep_avg -= run_time;
-	if ((long)prev->sleep_avg <= 0)
-		prev->sleep_avg = 0;
+	update_cpu_clock(prev, rq, now, 0);
 	prev->timestamp = prev->last_ran = now;
 
 	sched_info_switch(prev, next);
@@ -3844,29 +3817,22 @@ EXPORT_SYMBOL(sleep_on_timeout);
  */
 void rt_mutex_setprio(struct task_struct *p, int prio)
 {
-	struct prio_array *array;
 	unsigned long flags;
+	int queued, oldprio;
 	struct rq *rq;
-	int oldprio;
 
 	BUG_ON(prio < 0 || prio > MAX_PRIO);
 
 	rq = task_rq_lock(p, &flags);
 
 	oldprio = p->prio;
-	array = p->array;
-	if (array)
-		dequeue_task(p, array);
+	queued = task_queued(p);
+	if (queued)
+		dequeue_task(p, rq);
 	p->prio = prio;
 
-	if (array) {
-		/*
-		 * If changing to an RT priority then queue it
-		 * in the active array!
-		 */
-		if (rt_task(p))
-			array = rq->active;
-		enqueue_task(p, array);
+	if (queued) {
+		enqueue_task(p, rq);
 		/*
 		 * Reschedule if we are currently running on this runqueue and
 		 * our priority decreased, or if we are not currently running on
@@ -3875,8 +3841,8 @@ void rt_mutex_setprio(struct task_struct
 		if (task_running(rq, p)) {
 			if (p->prio > oldprio)
 				resched_task(rq->curr);
-		} else if (TASK_PREEMPTS_CURR(p, rq))
-			resched_task(rq->curr);
+		} else
+			try_preempt(p, rq);
 	}
 	task_rq_unlock(rq, &flags);
 }
@@ -3885,8 +3851,7 @@ void rt_mutex_setprio(struct task_struct
 
 void set_user_nice(struct task_struct *p, long nice)
 {
-	struct prio_array *array;
-	int old_prio, delta;
+	int queued, old_prio,delta;
 	unsigned long flags;
 	struct rq *rq;
 
@@ -3907,20 +3872,20 @@ void set_user_nice(struct task_struct *p
 		p->static_prio = NICE_TO_PRIO(nice);
 		goto out_unlock;
 	}
-	array = p->array;
-	if (array) {
-		dequeue_task(p, array);
+	queued = task_queued(p);
+	if (queued) {
+		dequeue_task(p, rq);
 		dec_raw_weighted_load(rq, p);
 	}
 
 	p->static_prio = NICE_TO_PRIO(nice);
-	set_load_weight(p);
 	old_prio = p->prio;
 	p->prio = effective_prio(p);
+	set_quota(p);
 	delta = p->prio - old_prio;
 
-	if (array) {
-		enqueue_task(p, array);
+	if (queued) {
+		enqueue_task(p, rq);
 		inc_raw_weighted_load(rq, p);
 		/*
 		 * If the task increased its priority or is running and
@@ -3996,7 +3961,7 @@ asmlinkage long sys_nice(int increment)
  *
  * This is the priority value as seen by users in /proc.
  * RT tasks are offset by -200. Normal tasks are centered
- * around 0, value goes from -16 to +15.
+ * around 0, value goes from 0 to +39.
  */
 int task_prio(const struct task_struct *p)
 {
@@ -4043,19 +4008,14 @@ static inline struct task_struct *find_p
 /* Actually do priority change: must hold rq lock. */
 static void __setscheduler(struct task_struct *p, int policy, int prio)
 {
-	BUG_ON(p->array);
+	BUG_ON(task_queued(p));
 
 	p->policy = policy;
 	p->rt_priority = prio;
 	p->normal_prio = normal_prio(p);
 	/* we are holding p->pi_lock already */
 	p->prio = rt_mutex_getprio(p);
-	/*
-	 * SCHED_BATCH tasks are treated as perpetual CPU hogs:
-	 */
-	if (policy == SCHED_BATCH)
-		p->sleep_avg = 0;
-	set_load_weight(p);
+	set_quota(p);
 }
 
 /**
@@ -4069,8 +4029,7 @@ static void __setscheduler(struct task_s
 int sched_setscheduler(struct task_struct *p, int policy,
 		       struct sched_param *param)
 {
-	int retval, oldprio, oldpolicy = -1;
-	struct prio_array *array;
+	int queued, retval, oldprio, oldpolicy = -1;
 	unsigned long flags;
 	struct rq *rq;
 
@@ -4144,12 +4103,12 @@ recheck:
 		spin_unlock_irqrestore(&p->pi_lock, flags);
 		goto recheck;
 	}
-	array = p->array;
-	if (array)
+	queued = task_queued(p);
+	if (queued)
 		deactivate_task(p, rq);
 	oldprio = p->prio;
 	__setscheduler(p, policy, param->sched_priority);
-	if (array) {
+	if (queued) {
 		__activate_task(p, rq);
 		/*
 		 * Reschedule if we are currently running on this runqueue and
@@ -4159,8 +4118,8 @@ recheck:
 		if (task_running(rq, p)) {
 			if (p->prio > oldprio)
 				resched_task(rq->curr);
-		} else if (TASK_PREEMPTS_CURR(p, rq))
-			resched_task(rq->curr);
+		} else
+			try_preempt(p, rq);
 	}
 	__task_rq_unlock(rq);
 	spin_unlock_irqrestore(&p->pi_lock, flags);
@@ -4433,40 +4392,27 @@ asmlinkage long sys_sched_getaffinity(pi
  * sys_sched_yield - yield the current processor to other threads.
  *
  * This function yields the current CPU by moving the calling thread
- * to the expired array. If there are no other threads running on this
- * CPU then this function will return.
+ * to the expired array if SCHED_NORMAL or the end of its current priority
+ * queue if a realtime task. If there are no other threads running on this
+ * cpu this function will return.
  */
 asmlinkage long sys_sched_yield(void)
 {
 	struct rq *rq = this_rq_lock();
-	struct prio_array *array = current->array, *target = rq->expired;
+	struct task_struct *p = current;
 
 	schedstat_inc(rq, yld_cnt);
-	/*
-	 * We implement yielding by moving the task into the expired
-	 * queue.
-	 *
-	 * (special rule: RT tasks will just roundrobin in the active
-	 *  array.)
-	 */
-	if (rt_task(current))
-		target = rq->active;
+	if (rq->nr_running == 1)
+		schedstat_inc(rq, yld_both_empty);
+	else {
+		struct prio_array *old_array = p->array;
+		int old_prio = p->prio;
 
-	if (array->nr_active == 1) {
-		schedstat_inc(rq, yld_act_empty);
-		if (!rq->expired->nr_active)
-			schedstat_inc(rq, yld_both_empty);
-	} else if (!rq->expired->nr_active)
-		schedstat_inc(rq, yld_exp_empty);
-
-	if (array != target) {
-		dequeue_task(current, array);
-		enqueue_task(current, target);
-	} else
-		/*
-		 * requeue_task is cheaper so perform that if possible.
-		 */
-		requeue_task(current, array);
+		/* p->prio will be updated in requeue_task via queue_expired */
+		if (!rt_task(p))
+			p->array = rq->expired;
+		requeue_task(p, rq, old_array, old_prio);
+	}
 
 	/*
 	 * Since we are going to call schedule() anyway, there's
@@ -4676,8 +4622,8 @@ long sys_sched_rr_get_interval(pid_t pid
 	if (retval)
 		goto out_unlock;
 
-	jiffies_to_timespec(p->policy == SCHED_FIFO ?
-				0 : task_timeslice(p), &t);
+	t = ns_to_timespec(p->policy == SCHED_FIFO ? 0 :
+			   MS_TO_NS(task_timeslice(p)));
 	read_unlock(&tasklist_lock);
 	retval = copy_to_user(interval, &t, sizeof(t)) ? -EFAULT : 0;
 out_nounlock:
@@ -4771,10 +4717,10 @@ void __cpuinit init_idle(struct task_str
 	struct rq *rq = cpu_rq(cpu);
 	unsigned long flags;
 
-	idle->timestamp = sched_clock();
-	idle->sleep_avg = 0;
-	idle->array = NULL;
-	idle->prio = idle->normal_prio = MAX_PRIO;
+	bitmap_zero(idle->bitmap, PRIO_RANGE);
+	idle->timestamp = idle->last_ran = sched_clock();
+	idle->array = rq->active;
+	idle->prio = idle->normal_prio = NICE_TO_PRIO(0);
 	idle->state = TASK_RUNNING;
 	idle->cpus_allowed = cpumask_of_cpu(cpu);
 	set_task_cpu(idle, cpu);
@@ -4893,7 +4839,7 @@ static int __migrate_task(struct task_st
 		goto out;
 
 	set_task_cpu(p, dest_cpu);
-	if (p->array) {
+	if (task_queued(p)) {
 		/*
 		 * Sync timestamp with rq_dest's before activating.
 		 * The same thing could be achieved by doing this step
@@ -4904,8 +4850,7 @@ static int __migrate_task(struct task_st
 				+ rq_dest->most_recent_timestamp;
 		deactivate_task(p, rq_src);
 		__activate_task(p, rq_dest);
-		if (TASK_PREEMPTS_CURR(p, rq_dest))
-			resched_task(rq_dest->curr);
+		try_preempt(p, rq_dest);
 	}
 	ret = 1;
 out:
@@ -5194,7 +5139,7 @@ migration_call(struct notifier_block *nf
 		/* Idle task back to normal (off runqueue, low prio) */
 		rq = task_rq_lock(rq->idle, &flags);
 		deactivate_task(rq->idle, rq);
-		rq->idle->static_prio = MAX_PRIO;
+		rq->idle->static_prio = NICE_TO_PRIO(0);
 		__setscheduler(rq->idle, SCHED_NORMAL, 0);
 		migrate_dead_tasks(cpu);
 		task_rq_unlock(rq, &flags);
@@ -6706,6 +6651,13 @@ void __init sched_init_smp(void)
 	/* Move init over to a non-isolated CPU */
 	if (set_cpus_allowed(current, non_isolated_cpus) < 0)
 		BUG();
+
+	/*
+	 * Assume that every added cpu gives us slightly less overall latency
+	 * allowing us to increase the base rr_interval, but in a non linear
+	 * fashion.
+	 */
+	rr_interval *= 1 + ilog2(num_online_cpus());
 }
 #else
 void __init sched_init_smp(void)
@@ -6727,6 +6679,16 @@ void __init sched_init(void)
 {
 	int i, j, k;
 
+	/* Generate the priority matrix */
+	for (i = 0; i < PRIO_RANGE; i++) {
+		bitmap_fill(prio_matrix[i], PRIO_RANGE);
+		j = PRIO_RANGE * PRIO_RANGE / (PRIO_RANGE - i);
+		for (k = 0; k <= PRIO_RANGE * (PRIO_RANGE - 1); k += j) {
+			__clear_bit(PRIO_RANGE - 1 - (k / PRIO_RANGE),
+				    prio_matrix[i]);
+		}
+	}
+
 	for_each_possible_cpu(i) {
 		struct prio_array *array;
 		struct rq *rq;
@@ -6735,11 +6697,16 @@ void __init sched_init(void)
 		spin_lock_init(&rq->lock);
 		lockdep_set_class(&rq->lock, &rq->rq_lock_key);
 		rq->nr_running = 0;
+		rq->prio_rotation = 0;
 		rq->active = rq->arrays;
 		rq->expired = rq->arrays + 1;
-		rq->best_expired_prio = MAX_PRIO;
+		reset_prio_levels(rq);
+		rq->dyn_bitmap = rq->active->prio_bitmap;
+		rq->exp_bitmap = rq->expired->prio_bitmap;
 
 #ifdef CONFIG_SMP
+		rq->active->rq = rq;
+		rq->expired->rq = rq;
 		rq->sd = NULL;
 		for (j = 1; j < 3; j++)
 			rq->cpu_load[j] = 0;
@@ -6752,16 +6719,16 @@ void __init sched_init(void)
 		atomic_set(&rq->nr_iowait, 0);
 
 		for (j = 0; j < 2; j++) {
+
 			array = rq->arrays + j;
-			for (k = 0; k < MAX_PRIO; k++) {
+			for (k = 0; k < MAX_PRIO; k++)
 				INIT_LIST_HEAD(array->queue + k);
-				__clear_bit(k, array->bitmap);
-			}
-			// delimiter for bitsearch
-			__set_bit(MAX_PRIO, array->bitmap);
+			bitmap_zero(array->prio_bitmap, MAX_PRIO);
+			/* delimiter for bitsearch */
+			__set_bit(MAX_PRIO, array->prio_bitmap);
 		}
-	}
 
+	}
 	set_load_weight(&init_task);
 
 #ifdef CONFIG_SMP
@@ -6815,10 +6782,10 @@ EXPORT_SYMBOL(__might_sleep);
 #ifdef CONFIG_MAGIC_SYSRQ
 void normalize_rt_tasks(void)
 {
-	struct prio_array *array;
 	struct task_struct *p;
 	unsigned long flags;
 	struct rq *rq;
+	int queued;
 
 	read_lock_irq(&tasklist_lock);
 	for_each_process(p) {
@@ -6828,11 +6795,11 @@ void normalize_rt_tasks(void)
 		spin_lock_irqsave(&p->pi_lock, flags);
 		rq = __task_rq_lock(p);
 
-		array = p->array;
-		if (array)
+		queued = task_queued(p);
+		if (queued)
 			deactivate_task(p, task_rq(p));
 		__setscheduler(p, SCHED_NORMAL, 0);
-		if (array) {
+		if (queued) {
 			__activate_task(p, task_rq(p));
 			resched_task(rq->curr);
 		}
Index: linux-2.6.21-ck2/Documentation/sysctl/kernel.txt
===================================================================
--- linux-2.6.21-ck2.orig/Documentation/sysctl/kernel.txt	2007-02-05 22:51:59.000000000 +1100
+++ linux-2.6.21-ck2/Documentation/sysctl/kernel.txt	2007-05-14 19:30:30.000000000 +1000
@@ -43,6 +43,7 @@ show up in /proc/sys/kernel:
 - printk
 - real-root-dev               ==> Documentation/initrd.txt
 - reboot-cmd                  [ SPARC only ]
+- rr_interval
 - rtsig-max
 - rtsig-nr
 - sem
@@ -288,6 +289,19 @@ rebooting. ???
 
 ==============================================================
 
+rr_interval:
+
+This is the smallest duration that any cpu process scheduling unit
+will run for. Increasing this value can increase throughput of cpu
+bound tasks substantially but at the expense of increased latencies
+overall. This value is in milliseconds and the default value chosen
+depends on the number of cpus available at scheduler initialisation
+with a minimum of 8.
+
+Valid values are from 1-5000.
+
+==============================================================
+
 rtsig-max & rtsig-nr:
 
 The file rtsig-max can be used to tune the maximum number
Index: linux-2.6.21-ck2/kernel/sysctl.c
===================================================================
--- linux-2.6.21-ck2.orig/kernel/sysctl.c	2007-05-03 22:20:57.000000000 +1000
+++ linux-2.6.21-ck2/kernel/sysctl.c	2007-05-14 19:30:30.000000000 +1000
@@ -76,6 +76,7 @@ extern int pid_max_min, pid_max_max;
 extern int sysctl_drop_caches;
 extern int percpu_pagelist_fraction;
 extern int compat_log;
+extern int rr_interval;
 
 /* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
 static int maxolduid = 65535;
@@ -159,6 +160,14 @@ int sysctl_legacy_va_layout;
 #endif
 
 
+/* Constants for minimum and maximum testing.
+   We use these as one-element integer vectors. */
+static int __read_mostly zero;
+static int __read_mostly one = 1;
+static int __read_mostly one_hundred = 100;
+static int __read_mostly five_thousand = 5000;
+
+
 /* The default sysctl tables: */
 
 static ctl_table root_table[] = {
@@ -499,6 +508,17 @@ static ctl_table kern_table[] = {
 		.mode		= 0444,
 		.proc_handler	= &proc_dointvec,
 	},
+	{
+		.ctl_name	= CTL_UNNUMBERED,
+		.procname	= "rr_interval",
+		.data		= &rr_interval,
+		.maxlen		= sizeof (int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec_minmax,
+		.strategy	= &sysctl_intvec,
+		.extra1		= &one,
+		.extra2		= &five_thousand,
+	},
 #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86)
 	{
 		.ctl_name       = KERN_UNKNOWN_NMI_PANIC,
@@ -607,12 +627,6 @@ static ctl_table kern_table[] = {
 	{ .ctl_name = 0 }
 };
 
-/* Constants for minimum and maximum testing in vm_table.
-   We use these as one-element integer vectors. */
-static int zero;
-static int one_hundred = 100;
-
-
 static ctl_table vm_table[] = {
 	{
 		.ctl_name	= VM_OVERCOMMIT_MEMORY,
Index: linux-2.6.21-ck2/fs/pipe.c
===================================================================
--- linux-2.6.21-ck2.orig/fs/pipe.c	2007-05-03 22:20:56.000000000 +1000
+++ linux-2.6.21-ck2/fs/pipe.c	2007-05-14 19:30:30.000000000 +1000
@@ -41,12 +41,7 @@ void pipe_wait(struct pipe_inode_info *p
 {
 	DEFINE_WAIT(wait);
 
-	/*
-	 * Pipes are system-local resources, so sleeping on them
-	 * is considered a noninteractive wait:
-	 */
-	prepare_to_wait(&pipe->wait, &wait,
-			TASK_INTERRUPTIBLE | TASK_NONINTERACTIVE);
+	prepare_to_wait(&pipe->wait, &wait, TASK_INTERRUPTIBLE);
 	if (pipe->inode)
 		mutex_unlock(&pipe->inode->i_mutex);
 	schedule();
Index: linux-2.6.21-ck2/Documentation/sched-design.txt
===================================================================
--- linux-2.6.21-ck2.orig/Documentation/sched-design.txt	2006-11-30 11:30:31.000000000 +1100
+++ linux-2.6.21-ck2/Documentation/sched-design.txt	2007-05-14 19:30:30.000000000 +1000
@@ -1,11 +1,14 @@
-		   Goals, Design and Implementation of the
-		      new ultra-scalable O(1) scheduler
+ Goals, Design and Implementation of the ultra-scalable O(1) scheduler by
+ Ingo Molnar and theStaircase Deadline cpu scheduler policy designed by
+ Con Kolivas.
 
 
-  This is an edited version of an email Ingo Molnar sent to
-  lkml on 4 Jan 2002.  It describes the goals, design, and
-  implementation of Ingo's new ultra-scalable O(1) scheduler.
-  Last Updated: 18 April 2002.
+  This was originally an edited version of an email Ingo Molnar sent to
+  lkml on 4 Jan 2002.  It describes the goals, design, and implementation
+  of Ingo's ultra-scalable O(1) scheduler. It now contains a description
+  of the Staircase Deadline priority scheduler that was built on this
+  design.
+  Last Updated: Fri, 4 May 2007
 
 
 Goal
@@ -163,3 +166,222 @@ certain code paths and data constructs. 
 code is smaller than the old one.
 
 	Ingo
+
+
+Staircase Deadline cpu scheduler policy
+================================================
+
+Design summary
+==============
+
+A novel design which incorporates a foreground-background descending priority
+system (the staircase) via a bandwidth allocation matrix according to nice
+level.
+
+
+Features
+========
+
+A starvation free, strict fairness O(1) scalable design with interactivity
+as good as the above restrictions can provide. There is no interactivity
+estimator, no sleep/run measurements and only simple fixed accounting.
+The design has strict enough a design and accounting that task behaviour
+can be modelled and maximum scheduling latencies can be predicted by
+the virtual deadline mechanism that manages runqueues. The prime concern
+in this design is to maintain fairness at all costs determined by nice level,
+yet to maintain as good interactivity as can be allowed within the
+constraints of strict fairness.
+
+
+Design description
+==================
+
+SD works off the principle of providing each task a quota of runtime that it is
+allowed to run at a number of priority levels determined by its static priority
+(ie. its nice level). If the task uses up its quota it has its priority
+decremented to the next level determined by a priority matrix. Once every
+runtime quota has been consumed of every priority level, a task is queued on the
+"expired" array. When no other tasks exist with quota, the expired array is
+activated and fresh quotas are handed out. This is all done in O(1).
+
+Design details
+==============
+
+Each task keeps a record of its own entitlement of cpu time. Most of the rest of
+these details apply to non-realtime tasks as rt task management is straight
+forward.
+
+Each runqueue keeps a record of what major epoch it is up to in the
+rq->prio_rotation field which is incremented on each major epoch. It also
+keeps a record of the current prio_level for each static priority task.
+
+Each task keeps a record of what major runqueue epoch it was last running
+on in p->rotation. It also keeps a record of what priority levels it has
+already been allocated quota from during this epoch in a bitmap p->bitmap.
+
+The only tunable that determines all other details is the RR_INTERVAL. This
+is set to 8ms, and is scaled gently upwards with more cpus. This value is
+tunable via a /proc interface.
+
+All tasks are initially given a quota based on RR_INTERVAL. This is equal to
+RR_INTERVAL between nice values of -6 and 0, half that size above nice 0, and
+progressively larger for nice values from -1 to -20. This is assigned to
+p->quota and only changes with changes in nice level.
+
+As a task is first queued, it checks in recalc_task_prio to see if it has run at
+this runqueue's current priority rotation. If it has not, it will have its
+p->prio level set according to the first slot in a "priority matrix" and will be
+given a p->time_slice equal to the p->quota, and has its allocation bitmap bit
+set in p->bitmap for this prio level. It is then queued on the current active
+priority array.
+
+If a task has already been running during this major epoch, and it has
+p->time_slice left and the rq->prio_quota for the task's p->prio still
+has quota, it will be placed back on the active array, but no more quota
+will be added.
+
+If a task has been running during this major epoch, but does not have
+p->time_slice left, it will find the next lowest priority in its bitmap that it
+has not been allocated quota from. It then gets the a full quota in
+p->time_slice. It is then queued on the current active priority array at the
+newly determined lower priority.
+
+If a task has been running during this major epoch, and does not have
+any entitlement left in p->bitmap and no time_slice left, it will have its
+bitmap cleared, and be queued at its best prio again, but on the expired
+priority array.
+
+When a task is queued, it has its relevant bit set in the array->prio_bitmap.
+
+p->time_slice is stored in nanosconds and is updated via update_cpu_clock on
+schedule() and scheduler_tick. If p->time_slice is below zero then the
+recalc_task_prio is readjusted and the task rescheduled.
+
+
+Priority Matrix
+===============
+
+In order to minimise the latencies between tasks of different nice levels
+running concurrently, the dynamic priority slots where different nice levels
+are queued are dithered instead of being sequential. What this means is that
+there are 40 priority slots where a task may run during one major rotation,
+and the allocation of slots is dependant on nice level. In the
+following table, a zero represents a slot where the task may run.
+
+PRIORITY:0..................20.................39
+nice -20 0000000000000000000000000000000000000000
+nice -10 1000100010001000100010001000100010010000
+nice   0 1010101010101010101010101010101010101010
+nice   5 1011010110110101101101011011010110110110
+nice  10 1110111011101110111011101110111011101110
+nice  15 1111111011111110111111101111111011111110
+nice  19 1111111111111111111111111111111111111110
+
+As can be seen, a nice -20 task runs in every priority slot whereas a nice 19
+task only runs one slot per major rotation. This dithered table allows for the
+smallest possible maximum latencies between tasks of varying nice levels, thus
+allowing vastly different nice levels to be used.
+
+SCHED_BATCH tasks are managed slightly differently, receiving only the top
+slots from its priority bitmap giving it equal cpu as SCHED_NORMAL, but
+slightly higher latencies.
+
+
+Modelling deadline behaviour
+============================
+
+As the accounting in this design is hard and not modified by sleep average
+calculations or interactivity modifiers, it is possible to accurately
+predict the maximum latency that a task may experience under different
+conditions. This is a virtual deadline mechanism enforced by mandatory
+timeslice expiration and not outside bandwidth measurement.
+
+The maximum duration a task can run during one major epoch is determined by its
+nice value. Nice 0 tasks can run at 19 different priority levels for RR_INTERVAL
+duration during each epoch. Nice 10 tasks can run at 9 priority levels for each
+epoch, and so on. The table in the priority matrix above demonstrates how this
+is enforced.
+
+Therefore the maximum duration a runqueue epoch can take is determined by
+the number of tasks running, and their nice level. After that, the maximum
+duration it can take before a task can wait before it get scheduled is
+determined by the position of its first slot on the matrix.
+
+In the following examples, these are _worst case scenarios_ and would rarely
+occur, but can be modelled nonetheless to determine the maximum possible
+latency.
+
+So for example, if two nice 0 tasks are running, and one has just expired as
+another is activated for the first time receiving a full quota for this
+runqueue rotation, the first task will wait:
+
+nr_tasks * max_duration + nice_difference * rr_interval
+1 * 19 * RR_INTERVAL + 0 = 152ms
+
+In the presence of a nice 10 task, a nice 0 task would wait a maximum of
+1 * 10 * RR_INTERVAL + 0 = 80ms
+
+In the presence of a nice 0 task, a nice 10 task would wait a maximum of
+1 * 19 * RR_INTERVAL + 1 * RR_INTERVAL = 160ms
+
+More useful than these values, though, are the average latencies which are
+a matter of determining the average distance between priority slots of
+different nice values and multiplying them by the tasks' quota. For example
+in the presence of a nice -10 task, a nice 0 task will wait either one or
+two slots. Given that nice -10 tasks have a quota 2.5 times the RR_INTERVAL,
+this means the latencies will alternate between 2.5 and 5 RR_INTERVALs or
+20 and 40ms respectively (on uniprocessor at 1000HZ).
+
+
+Achieving interactivity
+=======================
+
+A requirement of this scheduler design was to achieve good interactivity
+despite being a completely fair deadline based design. The disadvantage of
+designs that try to achieve interactivity is that they usually do so at
+the expense of maintaining fairness. As cpu speeds increase, the requirement
+for some sort of metered unfairness towards interactive tasks becomes a less
+desirable phenomenon, but low latency and fairness remains mandatory to
+good interactive performance.
+
+This design relies on the fact that interactive tasks, by their nature,
+sleep often. Most fair scheduling designs end up penalising such tasks
+indirectly giving them less than their fair possible share because of the
+sleep, and have to use a mechanism of bonusing their priority to offset
+this based on the duration they sleep. This becomes increasingly inaccurate
+as the number of running tasks rises and more tasks spend time waiting on
+runqueues rather than sleeping, and it is impossible to tell whether the
+task that's waiting on a runqueue only intends to run for a short period and
+then sleep again after than runqueue wait. Furthermore, all such designs rely
+on a period of time to pass to accumulate some form of statistic on the task
+before deciding on how much to give them preference. The shorter this period,
+the more rapidly bursts of cpu ruin the interactive tasks behaviour. The
+longer this period, the longer it takes for interactive tasks to get low
+scheduling latencies and fair cpu.
+
+This design does not measure sleep time at all. Interactive tasks that sleep
+often will wake up having consumed very little if any of their quota for
+the current major priority rotation. The longer they have slept, the less
+likely they are to even be on the current major priority rotation. Once
+woken up, though, they get to use up a their full quota for that epoch,
+whether part of a quota remains or a full quota. Overall, however, they
+can still only run as much cpu time for that epoch as any other task of the
+same nice level. This means that two tasks behaving completely differently
+from fully cpu bound to waking/sleeping extremely frequently will still
+get the same quota of cpu, but the latter will be using its quota for that
+epoch in bursts rather than continuously. This guarantees that interactive
+tasks get the same amount of cpu as cpu bound ones.
+
+The other requirement of interactive tasks is also to obtain low latencies
+for when they are scheduled. Unlike fully cpu bound tasks and the maximum
+latencies possible described in the modelling deadline behaviour section
+above, tasks that sleep will wake up with quota available usually at the
+current runqueue's priority_level or better. This means that the most latency
+they are likely to see is one RR_INTERVAL, and often they will preempt the
+current task if it is not of a sleeping nature. This then guarantees very
+low latency for interactive tasks, and the lowest latencies for the least
+cpu bound tasks.
+
+
+Fri, 4 May 2007
+Con Kolivas <kernel@kolivas.org>
Index: linux-2.6.21-ck2/kernel/softirq.c
===================================================================
--- linux-2.6.21-ck2.orig/kernel/softirq.c	2007-05-03 22:20:57.000000000 +1000
+++ linux-2.6.21-ck2/kernel/softirq.c	2007-05-14 19:30:30.000000000 +1000
@@ -488,7 +488,7 @@ void __init softirq_init(void)
 
 static int ksoftirqd(void * __bind_cpu)
 {
-	set_user_nice(current, 19);
+	set_user_nice(current, 15);
 	current->flags |= PF_NOFREEZE;
 
 	set_current_state(TASK_INTERRUPTIBLE);