Commit 840c5abc authored May 06, 2017 by Peter Zijlstra Committed by Ingo Molnar Sep 29, 2017

sched/fair: More accurate reweight_entity()



When a (group) entity changes it's weight we should instantly change
its load_avg and propagate that change into the sums it is part of.
Because we use these values to predict future behaviour and are not
interested in its historical value.

Without this change, the change in load would need to propagate
through the average, by which time it could again have changed etc..
always chasing itself.

With this change, the cfs_rq load_avg sum will more accurately reflect
the current runnable and expected return of blocked load.

Reported-by: Paul Turner <pjt@google.com>
[josef: compile fix !SMP || !FAIR_GROUP]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 8d5b9025

kernel/sched/fair.c

+11 −1

Original line number	Diff line number	Diff line
		@@ -2886,12 +2886,22 @@ static void reweight_entity(struct cfs_rq cfs_rq, struct sched_entity se,
		if (cfs_rq->curr == se)
		update_curr(cfs_rq);
		account_entity_dequeue(cfs_rq, se);
		dequeue_runnable_load_avg(cfs_rq, se);
		}
		dequeue_load_avg(cfs_rq, se);

		update_load_set(&se->load, weight);

		if (se->on_rq)
		#ifdef CONFIG_SMP
		se->avg.load_avg = div_u64(se_weight(se) * se->avg.load_sum,
		LOAD_AVG_MAX - 1024 + se->avg.period_contrib);
		#endif

		enqueue_load_avg(cfs_rq, se);
		if (se->on_rq) {
		account_entity_enqueue(cfs_rq, se);
		enqueue_runnable_load_avg(cfs_rq, se);
		}
		}

		static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);

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