mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-21 16:29:59 +00:00
![Linus Torvalds](/assets/img/avatar_default.png)
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
126 lines
4 KiB
Text
126 lines
4 KiB
Text
Reference for various scheduler-related methods in the O(1) scheduler
|
|
Robert Love <rml@tech9.net>, MontaVista Software
|
|
|
|
|
|
Note most of these methods are local to kernel/sched.c - this is by design.
|
|
The scheduler is meant to be self-contained and abstracted away. This document
|
|
is primarily for understanding the scheduler, not interfacing to it. Some of
|
|
the discussed interfaces, however, are general process/scheduling methods.
|
|
They are typically defined in include/linux/sched.h.
|
|
|
|
|
|
Main Scheduling Methods
|
|
-----------------------
|
|
|
|
void load_balance(runqueue_t *this_rq, int idle)
|
|
Attempts to pull tasks from one cpu to another to balance cpu usage,
|
|
if needed. This method is called explicitly if the runqueues are
|
|
inbalanced or periodically by the timer tick. Prior to calling,
|
|
the current runqueue must be locked and interrupts disabled.
|
|
|
|
void schedule()
|
|
The main scheduling function. Upon return, the highest priority
|
|
process will be active.
|
|
|
|
|
|
Locking
|
|
-------
|
|
|
|
Each runqueue has its own lock, rq->lock. When multiple runqueues need
|
|
to be locked, lock acquires must be ordered by ascending &runqueue value.
|
|
|
|
A specific runqueue is locked via
|
|
|
|
task_rq_lock(task_t pid, unsigned long *flags)
|
|
|
|
which disables preemption, disables interrupts, and locks the runqueue pid is
|
|
running on. Likewise,
|
|
|
|
task_rq_unlock(task_t pid, unsigned long *flags)
|
|
|
|
unlocks the runqueue pid is running on, restores interrupts to their previous
|
|
state, and reenables preemption.
|
|
|
|
The routines
|
|
|
|
double_rq_lock(runqueue_t *rq1, runqueue_t *rq2)
|
|
|
|
and
|
|
|
|
double_rq_unlock(runqueue_t *rq1, runqueue_t *rq2)
|
|
|
|
safely lock and unlock, respectively, the two specified runqueues. They do
|
|
not, however, disable and restore interrupts. Users are required to do so
|
|
manually before and after calls.
|
|
|
|
|
|
Values
|
|
------
|
|
|
|
MAX_PRIO
|
|
The maximum priority of the system, stored in the task as task->prio.
|
|
Lower priorities are higher. Normal (non-RT) priorities range from
|
|
MAX_RT_PRIO to (MAX_PRIO - 1).
|
|
MAX_RT_PRIO
|
|
The maximum real-time priority of the system. Valid RT priorities
|
|
range from 0 to (MAX_RT_PRIO - 1).
|
|
MAX_USER_RT_PRIO
|
|
The maximum real-time priority that is exported to user-space. Should
|
|
always be equal to or less than MAX_RT_PRIO. Setting it less allows
|
|
kernel threads to have higher priorities than any user-space task.
|
|
MIN_TIMESLICE
|
|
MAX_TIMESLICE
|
|
Respectively, the minimum and maximum timeslices (quanta) of a process.
|
|
|
|
Data
|
|
----
|
|
|
|
struct runqueue
|
|
The main per-CPU runqueue data structure.
|
|
struct task_struct
|
|
The main per-process data structure.
|
|
|
|
|
|
General Methods
|
|
---------------
|
|
|
|
cpu_rq(cpu)
|
|
Returns the runqueue of the specified cpu.
|
|
this_rq()
|
|
Returns the runqueue of the current cpu.
|
|
task_rq(pid)
|
|
Returns the runqueue which holds the specified pid.
|
|
cpu_curr(cpu)
|
|
Returns the task currently running on the given cpu.
|
|
rt_task(pid)
|
|
Returns true if pid is real-time, false if not.
|
|
|
|
|
|
Process Control Methods
|
|
-----------------------
|
|
|
|
void set_user_nice(task_t *p, long nice)
|
|
Sets the "nice" value of task p to the given value.
|
|
int setscheduler(pid_t pid, int policy, struct sched_param *param)
|
|
Sets the scheduling policy and parameters for the given pid.
|
|
int set_cpus_allowed(task_t *p, unsigned long new_mask)
|
|
Sets a given task's CPU affinity and migrates it to a proper cpu.
|
|
Callers must have a valid reference to the task and assure the
|
|
task not exit prematurely. No locks can be held during the call.
|
|
set_task_state(tsk, state_value)
|
|
Sets the given task's state to the given value.
|
|
set_current_state(state_value)
|
|
Sets the current task's state to the given value.
|
|
void set_tsk_need_resched(struct task_struct *tsk)
|
|
Sets need_resched in the given task.
|
|
void clear_tsk_need_resched(struct task_struct *tsk)
|
|
Clears need_resched in the given task.
|
|
void set_need_resched()
|
|
Sets need_resched in the current task.
|
|
void clear_need_resched()
|
|
Clears need_resched in the current task.
|
|
int need_resched()
|
|
Returns true if need_resched is set in the current task, false
|
|
otherwise.
|
|
yield()
|
|
Place the current process at the end of the runqueue and call schedule.
|