linux-kernel - Re: [RFC PATCH v2 2/2] scheduler: add scheduler level for clusters

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Message-ID: <20201203092831.GH2414@hirez.programming.kicks-ass.net>
Date:   Thu, 3 Dec 2020 10:28:31 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     Barry Song <song.bao.hua@...ilicon.com>, catalin.marinas@....com,
        will@...nel.org, rjw@...ysocki.net, lenb@...nel.org,
        gregkh@...uxfoundation.org, Jonathan.Cameron@...wei.com,
        mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        mark.rutland@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linuxarm@...wei.com, xuwei5@...wei.com, prime.zeng@...ilicon.com
Subject: Re: [RFC PATCH v2 2/2] scheduler: add scheduler level for clusters

On Tue, Dec 01, 2020 at 04:04:04PM +0000, Valentin Schneider wrote:
> 
> Gating this behind this new config only leveraged by arm64 doesn't make it
> very generic. Note that powerpc also has this newish "CACHE" level which
> seems to overlap in function with your "CLUSTER" one (both are arch
> specific, though).
> 
> I think what you are after here is an SD_SHARE_PKG_RESOURCES domain walk,
> i.e. scan CPUs by increasing cache "distance". We already have it in some
> form, as we scan SMT & LLC domains; AFAICT LLC always maps to MC, except
> for said powerpc's CACHE thingie.

There's some intel chips with a smaller L2, but I don't think we ever
bothered.

There's also the extended topology stuff from Intel: SMT, Core, Module,
Tile, Die, of which we've only partially used Die I think.

Whatever we do, it might make sense to not all use different names.

Also, I think Mel said he was cooking something for
select_idle_balance().

Also, I've previously posted patches that fold all the iterations into
one, so it might make sense to revisit some of that if Mel also already
didn.t