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

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Message-ID: <ebc9da1f1fdf45479651906edbfc55a6@hisilicon.com>
Date:   Thu, 3 Dec 2020 09:57:09 +0000
From:   "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>
CC:     "catalin.marinas@....com" <catalin.marinas@....com>,
        "will@...nel.org" <will@...nel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "dietmar.eggemann@....com" <dietmar.eggemann@....com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "bsegall@...gle.com" <bsegall@...gle.com>,
        "mgorman@...e.de" <mgorman@...e.de>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        Linuxarm <linuxarm@...wei.com>, "xuwei (O)" <xuwei5@...wei.com>,
        "Zengtao (B)" <prime.zeng@...ilicon.com>
Subject: RE: [RFC PATCH v2 2/2] scheduler: add scheduler level for clusters



> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Thursday, December 3, 2020 10:29 PM
> To: Valentin Schneider <valentin.schneider@....com>
> Cc: Song Bao Hua (Barry Song) <song.bao.hua@...ilicon.com>;
> catalin.marinas@....com; will@...nel.org; rjw@...ysocki.net; lenb@...nel.org;
> gregkh@...uxfoundation.org; Jonathan Cameron <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
> <linuxarm@...wei.com>; xuwei (O) <xuwei5@...wei.com>; Zengtao (B)
> <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.

Yep. Valentin was actually recommending the same SD_SHARE_PKG_RESOURCES sd flags
by ignoring the actual names of the hardware.
But the question is where we should start, in case we have 3 domains under llc,
maybe it is not good to scan from the first level domain as it is gathering
too much.

> 
> 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

Would you point out the link of your previous patches?

Thanks
Barry