linux-kernel - Re: [PATCH v2 2/2] sched/topology: Optimize topology_span

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Message-ID: <ZhhcPwFCgxDUhndo@DESKTOP-IR8JFSN.>
Date: Thu, 11 Apr 2024 16:55:11 -0500
From: Kyle Meyer <kyle.meyer@....com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, yury.norov@...il.com,
        linux@...musvillemoes.dk, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        russ.anderson@....com, dimitri.sivanich@....com, steve.wahl@....com
Subject: Re: [PATCH v2 2/2] sched/topology: Optimize topology_span_sane()

On Thu, Apr 11, 2024 at 01:38:46PM +0300, Andy Shevchenko wrote:
> On Wed, Apr 10, 2024 at 04:33:11PM -0500, Kyle Meyer wrote:
> > Optimize topology_span_sane() by removing duplicate comparisons.
> > 
> > Since topology_span_sane() is called inside of for_each_cpu(), each
> > pervious CPU has already been compared against every other CPU. The
> 
> previous

Thank you for pointing that out. Should I send an updated version or can
a maintainer correct my mistake?

> > current CPU only needs to be compared against higher-numbered CPUs.
> > 
> > The total number of comparisons is reduced from N * (N - 1) to
> > N * (N - 1) / 2 on each non-NUMA scheduling domain level.
> 
> Thank you, now it makes sense.

Thanks,
Kyle Meyer