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Message-ID: <ZlHSNXe0c5/sx9D9@chenyu5-mobl2>
Date: Sat, 25 May 2024 19:57:41 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: Mike Galbraith <efault@....de>
CC: Chunxin Zang <spring.cxz@...il.com>, <mingo@...hat.com>,
<peterz@...radead.org>, <juri.lelli@...hat.com>,
<vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
<rostedt@...dmis.org>, <bsegall@...gle.com>, <mgorman@...e.de>,
<bristot@...hat.com>, <vschneid@...hat.com>, <linux-kernel@...r.kernel.org>,
<yangchen11@...iang.com>, <zhouchunhua@...iang.com>,
<zangchunxin@...iang.com>
Subject: Re: [PATCH] sched/fair: Reschedule the cfs_rq when current is
ineligible
On 2024-05-25 at 08:41:28 +0200, Mike Galbraith wrote:
> On Fri, 2024-05-24 at 21:40 +0800, Chunxin Zang wrote:
> > I found that some tasks have been running for a long enough time and
> > have become illegal, but they are still not releasing the CPU. This
> > will increase the scheduling delay of other processes. Therefore, I
> > tried checking the current process in wakeup_preempt and entity_tick,
> > and if it is illegal, reschedule that cfs queue.
>
> My box gave making the XXX below reality a two thumbs up when fiddling
> with the original unfettered and a bit harsh RUN_TO_PARITY.
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8a5b1ae0aa55..922834f172b0 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8413,12 +8413,13 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
> update_curr(cfs_rq);
>
> /*
> - * XXX pick_eevdf(cfs_rq) != se ?
> + * Run @curr until it is no longer our best option. Basing the preempt
> + * decision on @curr reselection puts any previous decisions back on the
> + * table in context "now", including granularity preservation decisions
> + * by RUN_TO_PARITY.
> */
> - if (pick_eevdf(cfs_rq) == pse)
> - goto preempt;
> -
> - return;
> + if (pick_eevdf(cfs_rq) == se)
> + return;
>
I suppose this change benefits the overloaded scenario:
neither current nor the wakee is the best one.
before: current continues to run.
after: best se in the tree preempts current.
hackbench -g 12 -l 1000000000 & (480 tasks, 2x of the CPUs)
cyclictest --mlockall -D 1m -q
before:
T: 0 (15983) P: 0 I:1000 C: 43054 Min: 11 Act: 144 Avg: 627 Max: 11446
after:
T: 0 (16473) P: 0 I:1000 C: 49822 Min: 7 Act: 160 Avg: 388 Max: 10190
Min, Avg, Max latency all decreased.
thanks,
Chenyu
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