linux-kernel - Re: [PATCH RFC] sched/fair: fix sudden expiration of cfq quota in put_prev

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Date:	Tue, 7 Apr 2015 17:43:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Ben Segall <bsegall@...gle.com>,
	Roman Gushchin <klamm@...dex-team.ru>
Subject: Re: [PATCH RFC] sched/fair: fix sudden expiration of cfq quota in
 put_prev_task()

On Tue, Apr 07, 2015 at 06:32:47PM +0300, Konstantin Khlebnikov wrote:
> On 07.04.2015 18:12, Peter Zijlstra wrote:
> >On Tue, Apr 07, 2015 at 03:47:58PM +0200, Peter Zijlstra wrote:
> >>Lemme think a bit more on that.
> >
> >So going by 734ff2a71f9e ("sched/rt: Fix picking RT and DL tasks from
> >empty queue") something like this would be called for.
> >
> >---
> >  kernel/sched/fair.c | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> >
> >diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> >index fdae26eb7218..1e47f816c976 100644
> >--- a/kernel/sched/fair.c
> >+++ b/kernel/sched/fair.c
> >@@ -5175,6 +5175,21 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev)
> >  	return p;
> >  simple:
> >  	cfs_rq = &rq->cfs;
> 
> We don't need this if prev isn't from fair_sched_class:
> first "goto simple" should go directly to "if (!cfs_rq->nr_running)".

Just add that to the test here:

> >+	if (cfs_bandwidth_used()) {
> >+		/*
> >+		 * We may dequeue prev's cfs_rq in put_prev_task().
> >+		 * So, we update time before cfs_rq->nr_running check.
> >+		 */
> >+		if (prev->on_rq)
> >+			update_curr(cfs_rq);
> >+
> >+		se = &prev->se;
> >+		for_each_sched_entity(se) {
> 
> Probably update_curr() should be inside loop too?

Ah, yes, you're right.

> >+			cfs_rq = cfs_rq_of(se);
> >+			check_cfs_rq_runtime(cfs_rq);
> >+		}
> >+	}
> >  #endif
> >
> >  	if (!cfs_rq->nr_running)
> >
> 
> 
> -- 
> Konstantin
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