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From: Vincent Guittot <vincent.guittot@linaro.org>
Date: Thu, 4 Apr 2024 17:10:07 +0200
Message-ID: <CAKfTPtBFFSOzAfnJ4DLMdaaWh0FebJ30VJ9kZOET7br9juaRHQ@mail.gmail.com>
Subject: Re: [PATCH v3 1/3] sched/fair: allow disabling sched_balance_newidle
 with sched_relax_domain_level
To: Valentin Schneider <vschneid@redhat.com>
Cc: Vitalii Bursov <vitaly@bursov.com>, Ingo Molnar <mingo@redhat.com>, 
	Peter Zijlstra <peterz@infradead.org>, 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>, 
	Daniel Bristot de Oliveira <bristot@redhat.com>, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"

On Thu, 4 Apr 2024 at 16:14, Valentin Schneider <vschneid@redhat.com> wrote:
>
> On 03/04/24 16:28, Vitalii Bursov wrote:
> > Change relax_domain_level checks so that it would be possible
> > to include or exclude all domains from newidle balancing.
> >
> > This matches the behavior described in the documentation:
> >   -1   no request. use system default or follow request of others.
> >    0   no search.
> >    1   search siblings (hyperthreads in a core).
> >
> > "2" enables levels 0 and 1, level_max excludes the last (level_max)
> > level, and level_max+1 includes all levels.
> >
> > Fixes: 9ae7ab20b483 ("sched/topology: Don't set SD_BALANCE_WAKE on cpuset domain relax")
>
> Not that it matters too much, but wasn't the behaviour the same back then?
> i.e.
>
>         if (request < sd->level)
>                 sd->flags &= ~(SD_BALANCE_WAKE|SD_BALANCE_NEWIDLE);
>
> So if relax_domain_level=0 we wouldn't clear the flags on e.g. SMT
> (level=0)

Yes, I have been too quick: this patch [2019] was quite "old" and the
last one which changes the condition so I assumed it was the culprit

>
> AFAICT the docs & the code have always been misaligned:
>
>   4d5f35533fb9 ("sched, cpuset: customize sched domains, docs") [2008]
>   1d3504fcf560 ("sched, cpuset: customize sched domains, core") [2008]
>
> History nitpicking aside, I think this makes sense, but existing users are
> going to get a surprise...
>