From: peterz@infradead.org
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Jiang Biao <benbjiang@gmail.com>, Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
linux-kernel <linux-kernel@vger.kernel.org>,
Jiang Biao <benbjiang@tencent.com>
Subject: Re: [PATCH] sched/fair: avoid vruntime compensation for SCHED_IDLE task
Date: Thu, 20 Aug 2020 14:58:29 +0200 [thread overview]
Message-ID: <20200820125829.GT2674@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAKfTPtABCbEuYf3uup5ZODyPXpUqBjgM8A5gBQqM0cQGxWk5zw@mail.gmail.com>
On Thu, Aug 20, 2020 at 02:51:06PM +0200, Vincent Guittot wrote:
> On Thu, 20 Aug 2020 at 14:00, Jiang Biao <benbjiang@gmail.com> wrote:
> >
> > From: Jiang Biao <benbjiang@tencent.com>
> >
> > Vruntime compensation has been down in place_entity() to
> > boot the waking procedure for fair tasks. There is no need to
>
> s/boot/boost/ ?
>
> > do that for SCHED_IDLE task actually.
> >
> > Not compensating vruntime for SCHED_IDLE task could make
> > SCHED_IDLE task more harmless for normal tasks.
This is rather week. It would be much better if there's some actual data
to support this claim.
> > Signed-off-by: Jiang Biao <benbjiang@tencent.com>
> > ---
> > kernel/sched/fair.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 1a68a0536add..adff77676a0a 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -4115,7 +4115,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
> > vruntime += sched_vslice(cfs_rq, se);
> >
> > /* sleeps up to a single latency don't count. */
> > - if (!initial) {
> > + if (!initial && likely(!task_has_idle_policy(task_of(se)))) {
>
> What if se is not a task ?
Then we very much need it, because it might have fair tasks inside. I
suppose you could do something complicated with idle_h_nr_running, but
is all that really worth the effort?
> > unsigned long thresh = sysctl_sched_latency;
> >
> > /*
> > --
> > 2.21.0
> >
next prev parent reply other threads:[~2020-08-20 12:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-20 12:00 [PATCH] sched/fair: avoid vruntime compensation for SCHED_IDLE task Jiang Biao
2020-08-20 12:51 ` Vincent Guittot
2020-08-20 12:58 ` peterz [this message]
2020-08-20 13:15 ` Vincent Guittot
2020-08-20 13:43 ` peterz
2020-08-20 14:09 ` Vincent Guittot
2020-08-20 14:24 ` Jiang Biao
2020-08-23 7:33 ` Jiang Biao
2020-08-28 12:55 ` Vincent Guittot
2020-09-01 10:14 ` Jiang Biao
2020-09-01 13:04 ` Vincent Guittot
2020-09-01 14:19 ` Jiang Biao
2020-08-20 14:19 ` Jiang Biao
2020-08-20 14:15 ` Jiang Biao
2020-08-21 0:37 ` [sched/fair] 88d13f778f: WARNING:at_kernel/sched/fair.c:#place_entity kernel test robot
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