Commit 4a465e3e authored Aug 03, 2018 by Dietmar Eggemann Committed by Ingo Molnar Oct 02, 2018

sched/fair: Remove setting task's se->runnable_weight during PELT update



A CFS (SCHED_OTHER, SCHED_BATCH or SCHED_IDLE policy) task's
se->runnable_weight must always be in sync with its se->load.weight.

se->runnable_weight is set to se->load.weight when the task is
forked (init_entity_runnable_average()) or reniced (reweight_entity()).

There are two cases in set_load_weight() which since they currently only
set se->load.weight could lead to a situation in which se->load.weight
is different to se->runnable_weight for a CFS task:

(1) A task switches to SCHED_IDLE.

(2) A SCHED_FIFO, SCHED_RR or SCHED_DEADLINE task which has been reniced
    (during which only its static priority gets set) switches to
    SCHED_OTHER or SCHED_BATCH.

Set se->runnable_weight to se->load.weight in these two cases to prevent
this. This eliminates the need to explicitly set it to se->load.weight
during PELT updates in the CFS scheduler fastpath.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Perret <quentin.perret@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: http://lkml.kernel.org/r/20180803140538.1178-1-dietmar.eggemann@arm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent fdf5f315

kernel/sched/core.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -700,6 +700,7 @@ static void set_load_weight(struct task_struct *p, bool update_load)
		if (idle_policy(p->policy)) {
		load->weight = scale_load(WEIGHT_IDLEPRIO);
		load->inv_weight = WMULT_IDLEPRIO;
		p->se.runnable_weight = load->weight;
		return;
		}

		@@ -712,6 +713,7 @@ static void set_load_weight(struct task_struct *p, bool update_load)
		} else {
		load->weight = scale_load(sched_prio_to_weight[prio]);
		load->inv_weight = sched_prio_to_wmult[prio];
		p->se.runnable_weight = load->weight;
		}
		}

kernel/sched/pelt.c

+0 −6

Original line number	Diff line number	Diff line
		@@ -269,9 +269,6 @@ ___update_load_avg(struct sched_avg *sa, unsigned long load, unsigned long runna

		int __update_load_avg_blocked_se(u64 now, int cpu, struct sched_entity *se)
		{
		if (entity_is_task(se))
		se->runnable_weight = se->load.weight;

		if (___update_load_sum(now, cpu, &se->avg, 0, 0, 0)) {
		___update_load_avg(&se->avg, se_weight(se), se_runnable(se));
		return 1;
		@@ -282,9 +279,6 @@ int __update_load_avg_blocked_se(u64 now, int cpu, struct sched_entity *se)

		int __update_load_avg_se(u64 now, int cpu, struct cfs_rq cfs_rq, struct sched_entity se)
		{
		if (entity_is_task(se))
		se->runnable_weight = se->load.weight;

		if (___update_load_sum(now, cpu, &se->avg, !!se->on_rq, !!se->on_rq,
		cfs_rq->curr == se)) {

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