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

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Date:	Tue, 07 Apr 2015 18:32:47 +0300
From:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:	Peter Zijlstra <peterz@...radead.org>
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 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)".

> +
> +	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?

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


-- 
Konstantin
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