From: Vincent Guittot <vincent.guittot@linaro.org>
To: Quentin Perret <qperret@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Juri Lelli <juri.lelli@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
linux-kernel <linux-kernel@vger.kernel.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Qais Yousef <qais.yousef@arm.com>,
ktkhai@virtuozzo.com
Subject: Re: [PATCH 4/7] sched: Optimize pick_next_task()
Date: Fri, 8 Nov 2019 17:46:28 +0100 [thread overview]
Message-ID: <CAKfTPtBM_AKD7iMyPo6Wv=FOvG3bBaDvZLyrD=RZHrdUzaQNxg@mail.gmail.com> (raw)
In-Reply-To: <20191108143348.GB123156@google.com>
On Fri, 8 Nov 2019 at 15:33, Quentin Perret <qperret@google.com> wrote:
>
> On Friday 08 Nov 2019 at 14:15:57 (+0100), Peter Zijlstra wrote:
> > Ever since we moved the sched_class defenitions into their own files,
>
> s/defenitions/definitions
>
> > the constant expression {fair,idle}_sched_class.pick_next_task() is
> > not in fact a compile time constant anymore and results in an indirect
> > call (barring LTO).
> >
> > Fix that by exposing pick_next_task_{fair,idle}() directly, this gets
> > rid of the indirect call (and RETPOLINE) on the fast path.
> >
> > Also remove the unlikely() from the idle case, it is in fact /the/ way
> > we select idle -- and that is a very common thing to do.
>
> I assumed this was to optimize the case where we did find a cfs task to
> run. That is, we can afford to hit the unlikely case when there is no
> work to do after, but when there is, we shouldn't spend time checking
> the idle case. Makes sense ?
I have the same understanding as Quentin
>
> Thanks,
> Quentin
next prev parent reply other threads:[~2019-11-08 16:46 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-08 13:15 [PATCH 0/7] scheduler patches Peter Zijlstra
2019-11-08 13:15 ` [PATCH 1/7] sched: Fix pick_next_task() vs change pattern race Peter Zijlstra
2019-11-08 14:28 ` Quentin Perret
2019-11-08 16:05 ` Valentin Schneider
2019-11-08 20:49 ` Peter Zijlstra
2019-11-08 17:03 ` Qais Yousef
2019-11-08 13:15 ` [PATCH 2/7] sched/fair: Better document newidle_balance() Peter Zijlstra
2019-11-11 9:32 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2019-11-08 13:15 ` [PATCH 3/7] sched: Make pick_next_task_idle() more consistent Peter Zijlstra
2019-11-11 9:32 ` [tip: sched/core] sched/core: " tip-bot2 for Peter Zijlstra
2019-11-08 13:15 ` [PATCH 4/7] sched: Optimize pick_next_task() Peter Zijlstra
2019-11-08 14:33 ` Quentin Perret
2019-11-08 16:46 ` Vincent Guittot [this message]
2019-11-08 20:46 ` Peter Zijlstra
2019-11-11 9:32 ` [tip: sched/core] sched/core: " tip-bot2 for Peter Zijlstra
2019-11-08 13:15 ` [PATCH 5/7] sched: Simplify sched_class::pick_next_task() Peter Zijlstra
2019-11-11 9:32 ` [tip: sched/core] sched/core: " tip-bot2 for Peter Zijlstra
2019-11-08 13:15 ` [PATCH 6/7] sched/fair: Use mul_u32_u32() Peter Zijlstra
2019-11-11 9:32 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2019-11-08 13:16 ` [PATCH 7/7] sched: Further clarify sched_class::set_next_task() Peter Zijlstra
2019-11-11 9:32 ` [tip: sched/core] sched/core: " tip-bot2 for Peter Zijlstra
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