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Commit e9c84311 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: Add TASK_WAKING 



We're going to want to drop rq->lock in try_to_wake_up() for a
longer period of time, however we also want to deal with concurrent
waking of the same task, which is currently handled by holding
rq->lock.

So introduce a new TASK state, namely TASK_WAKING, which indicates
someone is already waking the task (other wakers will fail p->state
& state).

We also keep preemption disabled over the whole ttwu().

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 5f3edc1b

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -190,6 +190,7 @@ extern unsigned long long time_sync_thresh; 
/* in tsk->state again */

#define TASK_DEAD		64

#define TASK_WAKEKILL		128

#define TASK_WAKING		256



/* Convenience macros for the sake of set_task_state */

#define TASK_KILLABLE		(TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)

kernel/sched.c

+15 −16
Original line number Diff line number Diff line
@@ -2310,7 +2310,6 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync) 
{

	int cpu, orig_cpu, this_cpu, success = 0;

	unsigned long flags;

	long old_state;

	struct rq *rq;



	if (!sched_feat(SYNC_WAKEUPS))
@@ -2332,11 +2331,12 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync) 
	}

#endif



	this_cpu = get_cpu();



	smp_wmb();

	rq = task_rq_lock(p, &flags);

	update_rq_clock(rq);

	old_state = p->state;

	if (!(old_state & state))

	if (!(p->state & state))

		goto out;



	if (p->se.on_rq)
@@ -2344,27 +2344,25 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync) 


	cpu = task_cpu(p);

	orig_cpu = cpu;

	this_cpu = smp_processor_id();



#ifdef CONFIG_SMP

	if (unlikely(task_running(rq, p)))

		goto out_activate;



	/*

	 * In order to handle concurrent wakeups and release the rq->lock

	 * we put the task in TASK_WAKING state.

	 */

	p->state = TASK_WAKING;

	task_rq_unlock(rq, &flags);



	cpu = p->sched_class->select_task_rq(p, SD_BALANCE_WAKE, sync);

	if (cpu != orig_cpu) {

	if (cpu != orig_cpu)

		set_task_cpu(p, cpu);

		task_rq_unlock(rq, &flags);

		/* might preempt at this point */

		rq = task_rq_lock(p, &flags);

		old_state = p->state;

		if (!(old_state & state))

			goto out;

		if (p->se.on_rq)

			goto out_running;



		this_cpu = smp_processor_id();

	rq = task_rq_lock(p, &flags);

	WARN_ON(p->state != TASK_WAKING);

	cpu = task_cpu(p);

	}



#ifdef CONFIG_SCHEDSTATS

	schedstat_inc(rq, ttwu_count);
@@ -2422,6 +2420,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync) 
#endif

out:

	task_rq_unlock(rq, &flags);

	put_cpu();



	return success;

}