From: Peter Zijlstra <peterz@infradead.org>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: Scott Wood <swood@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Rik van Riel <riel@surriel.com>, Mel Gorman <mgorman@suse.de>,
linux-kernel@vger.kernel.org,
linux-rt-users <linux-rt-users@vger.kernel.org>
Subject: Re: [RFC PATCH 1/3] sched/fair: Call newidle_balance() from finish_task_switch()
Date: Wed, 29 Apr 2020 00:09:17 +0200 [thread overview]
Message-ID: <20200428220917.GB16027@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <jhjftcns35d.mognet@arm.com>
On Tue, Apr 28, 2020 at 10:37:18PM +0100, Valentin Schneider wrote:
>
> On 28/04/20 06:02, Scott Wood wrote:
> > Thus, newidle_balance() is entered with interrupts enabled, which allows
> > (in the next patch) enabling interrupts when the lock is dropped.
> >
> > Signed-off-by: Scott Wood <swood@redhat.com>
> > ---
> > kernel/sched/core.c | 7 ++++---
> > kernel/sched/fair.c | 45 ++++++++++++++++----------------------------
> > kernel/sched/sched.h | 6 ++----
> > 3 files changed, 22 insertions(+), 36 deletions(-)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 9a2fbf98fd6f..0294beb8d16c 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -3241,6 +3241,10 @@ static struct rq *finish_task_switch(struct task_struct *prev)
> > }
> >
> > tick_nohz_task_switch();
> > +
> > + if (is_idle_task(current))
> > + newidle_balance();
> > +
>
> This means we must go through a switch_to(idle) before figuring out we
> could've switched to a CFS task, and do it then. I'm curious to see the
> performance impact of that.
Also, if you move it this late, this is entirely the wrong place. If you
do it after the context switch either use the balance_callback or put it
in the idle path.
But what Valentin said; this needs a fair bit of support, the whole
reason we've never done this is to avoid that double context switch...
next prev parent reply other threads:[~2020-04-28 22:09 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-28 5:02 [RFC PATCH 0/3] newidle_balance() latency mitigation Scott Wood
2020-04-28 5:02 ` [RFC PATCH 1/3] sched/fair: Call newidle_balance() from finish_task_switch() Scott Wood
2020-04-28 21:37 ` Valentin Schneider
2020-04-28 22:09 ` Peter Zijlstra [this message]
2020-04-28 22:55 ` Scott Wood
2020-04-28 23:02 ` Peter Zijlstra
2020-04-28 23:20 ` Scott Wood
2020-04-29 9:05 ` Peter Zijlstra
2020-04-30 1:31 ` Scott Wood
2020-05-11 10:58 ` Peter Zijlstra
2020-05-11 12:13 ` Peter Zijlstra
2020-04-28 22:33 ` Scott Wood
2020-04-29 12:00 ` Valentin Schneider
2020-04-29 8:27 ` Vincent Guittot
2020-04-30 1:36 ` Scott Wood
2020-04-28 5:02 ` [RFC PATCH 2/3] sched/fair: Enable interrupts when dropping lock in newidle_balance() Scott Wood
2020-04-28 5:02 ` [RFC PATCH 3/3] sched,rt: break out of load balancing if an RT task appears Scott Wood
2020-04-28 21:56 ` Valentin Schneider
2020-04-28 22:33 ` Scott Wood
2020-04-28 22:52 ` Scott Wood
2020-04-29 12:01 ` Valentin Schneider
2020-04-28 13:27 ` [RFC PATCH 0/3] newidle_balance() latency mitigation Steven Rostedt
2020-04-29 23:13 ` Valentin Schneider
2020-04-30 7:44 ` Vincent Guittot
2020-04-30 10:14 ` Valentin Schneider
2020-04-30 12:42 ` Vincent Guittot
2020-04-30 13:56 ` Valentin Schneider
2020-04-30 12:48 ` Vincent Guittot
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