Contents of /alx-src/tags/kernel26-2.6.12-alx-r9/Documentation/sched-coding.txt
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Wed Mar 4 11:03:09 2009 UTC (15 years, 3 months ago) by niro
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Tag kernel26-2.6.12-alx-r9
1 | Reference for various scheduler-related methods in the O(1) scheduler |
2 | Robert Love <rml@tech9.net>, MontaVista Software |
3 | |
4 | |
5 | Note most of these methods are local to kernel/sched.c - this is by design. |
6 | The scheduler is meant to be self-contained and abstracted away. This document |
7 | is primarily for understanding the scheduler, not interfacing to it. Some of |
8 | the discussed interfaces, however, are general process/scheduling methods. |
9 | They are typically defined in include/linux/sched.h. |
10 | |
11 | |
12 | Main Scheduling Methods |
13 | ----------------------- |
14 | |
15 | void load_balance(runqueue_t *this_rq, int idle) |
16 | Attempts to pull tasks from one cpu to another to balance cpu usage, |
17 | if needed. This method is called explicitly if the runqueues are |
18 | inbalanced or periodically by the timer tick. Prior to calling, |
19 | the current runqueue must be locked and interrupts disabled. |
20 | |
21 | void schedule() |
22 | The main scheduling function. Upon return, the highest priority |
23 | process will be active. |
24 | |
25 | |
26 | Locking |
27 | ------- |
28 | |
29 | Each runqueue has its own lock, rq->lock. When multiple runqueues need |
30 | to be locked, lock acquires must be ordered by ascending &runqueue value. |
31 | |
32 | A specific runqueue is locked via |
33 | |
34 | task_rq_lock(task_t pid, unsigned long *flags) |
35 | |
36 | which disables preemption, disables interrupts, and locks the runqueue pid is |
37 | running on. Likewise, |
38 | |
39 | task_rq_unlock(task_t pid, unsigned long *flags) |
40 | |
41 | unlocks the runqueue pid is running on, restores interrupts to their previous |
42 | state, and reenables preemption. |
43 | |
44 | The routines |
45 | |
46 | double_rq_lock(runqueue_t *rq1, runqueue_t *rq2) |
47 | |
48 | and |
49 | |
50 | double_rq_unlock(runqueue_t *rq1, runqueue_t *rq2) |
51 | |
52 | safely lock and unlock, respectively, the two specified runqueues. They do |
53 | not, however, disable and restore interrupts. Users are required to do so |
54 | manually before and after calls. |
55 | |
56 | |
57 | Values |
58 | ------ |
59 | |
60 | MAX_PRIO |
61 | The maximum priority of the system, stored in the task as task->prio. |
62 | Lower priorities are higher. Normal (non-RT) priorities range from |
63 | MAX_RT_PRIO to (MAX_PRIO - 1). |
64 | MAX_RT_PRIO |
65 | The maximum real-time priority of the system. Valid RT priorities |
66 | range from 0 to (MAX_RT_PRIO - 1). |
67 | MAX_USER_RT_PRIO |
68 | The maximum real-time priority that is exported to user-space. Should |
69 | always be equal to or less than MAX_RT_PRIO. Setting it less allows |
70 | kernel threads to have higher priorities than any user-space task. |
71 | MIN_TIMESLICE |
72 | MAX_TIMESLICE |
73 | Respectively, the minimum and maximum timeslices (quanta) of a process. |
74 | |
75 | Data |
76 | ---- |
77 | |
78 | struct runqueue |
79 | The main per-CPU runqueue data structure. |
80 | struct task_struct |
81 | The main per-process data structure. |
82 | |
83 | |
84 | General Methods |
85 | --------------- |
86 | |
87 | cpu_rq(cpu) |
88 | Returns the runqueue of the specified cpu. |
89 | this_rq() |
90 | Returns the runqueue of the current cpu. |
91 | task_rq(pid) |
92 | Returns the runqueue which holds the specified pid. |
93 | cpu_curr(cpu) |
94 | Returns the task currently running on the given cpu. |
95 | rt_task(pid) |
96 | Returns true if pid is real-time, false if not. |
97 | |
98 | |
99 | Process Control Methods |
100 | ----------------------- |
101 | |
102 | void set_user_nice(task_t *p, long nice) |
103 | Sets the "nice" value of task p to the given value. |
104 | int setscheduler(pid_t pid, int policy, struct sched_param *param) |
105 | Sets the scheduling policy and parameters for the given pid. |
106 | int set_cpus_allowed(task_t *p, unsigned long new_mask) |
107 | Sets a given task's CPU affinity and migrates it to a proper cpu. |
108 | Callers must have a valid reference to the task and assure the |
109 | task not exit prematurely. No locks can be held during the call. |
110 | set_task_state(tsk, state_value) |
111 | Sets the given task's state to the given value. |
112 | set_current_state(state_value) |
113 | Sets the current task's state to the given value. |
114 | void set_tsk_need_resched(struct task_struct *tsk) |
115 | Sets need_resched in the given task. |
116 | void clear_tsk_need_resched(struct task_struct *tsk) |
117 | Clears need_resched in the given task. |
118 | void set_need_resched() |
119 | Sets need_resched in the current task. |
120 | void clear_need_resched() |
121 | Clears need_resched in the current task. |
122 | int need_resched() |
123 | Returns true if need_resched is set in the current task, false |
124 | otherwise. |
125 | yield() |
126 | Place the current process at the end of the runqueue and call schedule. |