linux-rt-users.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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...

  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200428220917.GB16027@hirez.programming.kicks-ass.net \
    --to=peterz@infradead.org \
    --cc=dietmar.eggemann@arm.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-rt-users@vger.kernel.org \
    --cc=mgorman@suse.de \
    --cc=mingo@redhat.com \
    --cc=riel@surriel.com \
    --cc=rostedt@goodmis.org \
    --cc=swood@redhat.com \
    --cc=valentin.schneider@arm.com \
    --cc=vincent.guittot@linaro.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).