127 lines
4.0 KiB
Plaintext
127 lines
4.0 KiB
Plaintext
Reference for various scheduler-related methods in the O(1) scheduler
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Robert Love <rml@tech9.net>, MontaVista Software
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Note most of these methods are local to kernel/sched.c - this is by design.
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The scheduler is meant to be self-contained and abstracted away. This document
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is primarily for understanding the scheduler, not interfacing to it. Some of
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the discussed interfaces, however, are general process/scheduling methods.
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They are typically defined in include/linux/sched.h.
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Main Scheduling Methods
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-----------------------
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void load_balance(runqueue_t *this_rq, int idle)
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Attempts to pull tasks from one cpu to another to balance cpu usage,
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if needed. This method is called explicitly if the runqueues are
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imbalanced or periodically by the timer tick. Prior to calling,
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the current runqueue must be locked and interrupts disabled.
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void schedule()
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The main scheduling function. Upon return, the highest priority
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process will be active.
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Locking
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-------
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Each runqueue has its own lock, rq->lock. When multiple runqueues need
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to be locked, lock acquires must be ordered by ascending &runqueue value.
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A specific runqueue is locked via
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task_rq_lock(task_t pid, unsigned long *flags)
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which disables preemption, disables interrupts, and locks the runqueue pid is
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running on. Likewise,
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task_rq_unlock(task_t pid, unsigned long *flags)
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unlocks the runqueue pid is running on, restores interrupts to their previous
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state, and reenables preemption.
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The routines
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double_rq_lock(runqueue_t *rq1, runqueue_t *rq2)
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and
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double_rq_unlock(runqueue_t *rq1, runqueue_t *rq2)
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safely lock and unlock, respectively, the two specified runqueues. They do
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not, however, disable and restore interrupts. Users are required to do so
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manually before and after calls.
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Values
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------
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MAX_PRIO
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The maximum priority of the system, stored in the task as task->prio.
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Lower priorities are higher. Normal (non-RT) priorities range from
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MAX_RT_PRIO to (MAX_PRIO - 1).
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MAX_RT_PRIO
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The maximum real-time priority of the system. Valid RT priorities
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range from 0 to (MAX_RT_PRIO - 1).
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MAX_USER_RT_PRIO
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The maximum real-time priority that is exported to user-space. Should
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always be equal to or less than MAX_RT_PRIO. Setting it less allows
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kernel threads to have higher priorities than any user-space task.
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MIN_TIMESLICE
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MAX_TIMESLICE
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Respectively, the minimum and maximum timeslices (quanta) of a process.
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Data
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----
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struct runqueue
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The main per-CPU runqueue data structure.
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struct task_struct
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The main per-process data structure.
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General Methods
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---------------
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cpu_rq(cpu)
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Returns the runqueue of the specified cpu.
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this_rq()
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Returns the runqueue of the current cpu.
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task_rq(pid)
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Returns the runqueue which holds the specified pid.
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cpu_curr(cpu)
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Returns the task currently running on the given cpu.
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rt_task(pid)
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Returns true if pid is real-time, false if not.
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Process Control Methods
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-----------------------
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void set_user_nice(task_t *p, long nice)
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Sets the "nice" value of task p to the given value.
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int setscheduler(pid_t pid, int policy, struct sched_param *param)
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Sets the scheduling policy and parameters for the given pid.
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int set_cpus_allowed(task_t *p, unsigned long new_mask)
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Sets a given task's CPU affinity and migrates it to a proper cpu.
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Callers must have a valid reference to the task and assure the
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task not exit prematurely. No locks can be held during the call.
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set_task_state(tsk, state_value)
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Sets the given task's state to the given value.
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set_current_state(state_value)
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Sets the current task's state to the given value.
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void set_tsk_need_resched(struct task_struct *tsk)
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Sets need_resched in the given task.
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void clear_tsk_need_resched(struct task_struct *tsk)
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Clears need_resched in the given task.
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void set_need_resched()
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Sets need_resched in the current task.
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void clear_need_resched()
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Clears need_resched in the current task.
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int need_resched()
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Returns true if need_resched is set in the current task, false
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otherwise.
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yield()
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Place the current process at the end of the runqueue and call schedule.
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