Commit ad4b78bb authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: Add new wakeup preemption mode: WAKEUP_RUNNING 



Create a new wakeup preemption mode, preempt towards tasks that run
shorter on avg. It sets next buddy to be sure we actually run the task
we preempted for.

Test results:

 root@twins:~# while :; do :; done &
 [1] 6537
 root@twins:~# while :; do :; done &
 [2] 6538
 root@twins:~# while :; do :; done &
 [3] 6539
 root@twins:~# while :; do :; done &
 [4] 6540

 root@twins:/home/peter# ./latt -c4 sleep 4
 Entries: 48 (clients=4)

 Averages:
 ------------------------------
        Max          4750 usec
        Avg           497 usec
        Stdev         737 usec

 root@twins:/home/peter# echo WAKEUP_RUNNING > /debug/sched_features

 root@twins:/home/peter# ./latt -c4 sleep 4
 Entries: 48 (clients=4)

 Averages:
 ------------------------------
        Max            14 usec
        Avg             5 usec
        Stdev           3 usec

Disabled by default - needs more testing.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: default avatarMike Galbraith <efault@gmx.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
LKML-Reference: <new-submission>
parent eb24073b

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -1113,6 +1113,8 @@ struct sched_entity { 
	u64			start_runtime;

	u64			avg_wakeup;



	u64			avg_running;



#ifdef CONFIG_SCHEDSTATS

	u64			wait_start;

	u64			wait_max;

kernel/sched.c

+10 −7
Original line number Diff line number Diff line
@@ -2458,6 +2458,7 @@ static void __sched_fork(struct task_struct *p) 
	p->se.avg_overlap		= 0;

	p->se.start_runtime		= 0;

	p->se.avg_wakeup		= sysctl_sched_wakeup_granularity;

	p->se.avg_running		= 0;



#ifdef CONFIG_SCHEDSTATS

	p->se.wait_start			= 0;
@@ -5310,14 +5311,13 @@ static inline void schedule_debug(struct task_struct *prev) 
#endif

}



static void put_prev_task(struct rq *rq, struct task_struct *prev)

static void put_prev_task(struct rq *rq, struct task_struct *p)

{

	if (prev->state == TASK_RUNNING) {

		u64 runtime = prev->se.sum_exec_runtime;

	u64 runtime = p->se.sum_exec_runtime - p->se.prev_sum_exec_runtime;



		runtime -= prev->se.prev_sum_exec_runtime;

		runtime = min_t(u64, runtime, 2*sysctl_sched_migration_cost);

	update_avg(&p->se.avg_running, runtime);



	if (p->state == TASK_RUNNING) {

		/*

		 * In order to avoid avg_overlap growing stale when we are

		 * indeed overlapping and hence not getting put to sleep, grow
@@ -5327,9 +5327,12 @@ static void put_prev_task(struct rq *rq, struct task_struct *prev) 
		 * correlates to the amount of cache footprint a task can

		 * build up.

		 */

		update_avg(&prev->se.avg_overlap, runtime);

		runtime = min_t(u64, runtime, 2*sysctl_sched_migration_cost);

		update_avg(&p->se.avg_overlap, runtime);

	} else {

		update_avg(&p->se.avg_running, 0);

	}

	prev->sched_class->put_prev_task(rq, prev);

	p->sched_class->put_prev_task(rq, p);

}



/*

kernel/sched_debug.c

+1 −0
Original line number Diff line number Diff line
@@ -395,6 +395,7 @@ void proc_sched_show_task(struct task_struct *p, struct seq_file *m) 
	PN(se.sum_exec_runtime);

	PN(se.avg_overlap);

	PN(se.avg_wakeup);

	PN(se.avg_running);



	nr_switches = p->nvcsw + p->nivcsw;

kernel/sched_fair.c

+11 −3
Original line number Diff line number Diff line
@@ -1605,9 +1605,6 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_ 
		return;

	}



	if (!sched_feat(WAKEUP_PREEMPT))

		return;



	if ((sched_feat(WAKEUP_SYNC) && sync) ||

	    (sched_feat(WAKEUP_OVERLAP) &&

	     (se->avg_overlap < sysctl_sched_migration_cost &&
@@ -1616,6 +1613,17 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_ 
		return;

	}



	if (sched_feat(WAKEUP_RUNNING)) {

		if (pse->avg_running < se->avg_running) {

			set_next_buddy(pse);

			resched_task(curr);

			return;

		}

	}



	if (!sched_feat(WAKEUP_PREEMPT))

		return;



	find_matching_se(&se, &pse);



	BUG_ON(!pse);

kernel/sched_features.h

+5 −0
Original line number Diff line number Diff line
@@ -53,6 +53,11 @@ SCHED_FEAT(WAKEUP_SYNC, 0) 
 */

SCHED_FEAT(WAKEUP_OVERLAP, 0)



/*

 * Wakeup preemption towards tasks that run short

 */

SCHED_FEAT(WAKEUP_RUNNING, 0)



/*

 * Use the SYNC wakeup hint, pipes and the likes use this to indicate

 * the remote end is likely to consume the data we just wrote, and

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