linux-kernel - Re: [PATCH v3 1/3] sched/fair: allow disabling sched_balance_newidle with sched_relax_domain

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Date: Thu, 04 Apr 2024 16:14:18 +0200
From: Valentin Schneider <vschneid@...hat.com>
To: Vitalii Bursov <vitaly@...sov.com>, Ingo Molnar <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann
 <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Ben
 Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, Daniel Bristot
 de Oliveira <bristot@...hat.com>, linux-kernel@...r.kernel.org, Vitalii
 Bursov <vitaly@...sov.com>
Subject: Re: [PATCH v3 1/3] sched/fair: allow disabling
 sched_balance_newidle with sched_relax_domain_level

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)

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...