From: Vincent Guittot <vincent.guittot@linaro.org>
To: Peter Zijlstra <peterz@infradead.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 15:15:32 +0200 [thread overview]
Message-ID: <CAKfTPtBuZOb9-W5sS=DqxcuMFa8Lw=7XqMJ_YrXEgd5zvufYjA@mail.gmail.com> (raw)
In-Reply-To: <20200820125829.GT2674@hirez.programming.kicks-ass.net>
On Thu, 20 Aug 2020 at 14:58, <peterz@infradead.org> wrote:
>
> 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?
Not sure that Jiang is using cgroups otherwise he would have seen a
warning I think.
That's been said, not compensating the vruntime for a sched_idle task
makes sense for me. Even if that will only help for others task in the
same cfs_rq
>
> > > unsigned long thresh = sysctl_sched_latency;
> > >
> > > /*
> > > --
> > > 2.21.0
> > >
next prev parent reply other threads:[~2020-08-20 13:16 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
2020-08-20 13:15 ` Vincent Guittot [this message]
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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