[RFC PATCH v2 2/2] scheduler: add scheduler level for clusters

[Song Bao Hua (Barry Song)]

> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz at infradead.org]
> Sent: Thursday, December 3, 2020 10:29 PM
> To: Valentin Schneider <valentin.schneider at arm.com>
> Cc: Song Bao Hua (Barry Song) <song.bao.hua at hisilicon.com>;
> catalin.marinas at arm.com; will at kernel.org; rjw at rjwysocki.net; lenb at kernel.org;
> gregkh at linuxfoundation.org; Jonathan Cameron <jonathan.cameron at huawei.com>;
> mingo at redhat.com; juri.lelli at redhat.com; vincent.guittot at linaro.org;
> dietmar.eggemann at arm.com; rostedt at goodmis.org; bsegall at google.com;
> mgorman at suse.de; mark.rutland at arm.com; linux-arm-kernel at lists.infradead.org;
> linux-kernel at vger.kernel.org; linux-acpi at vger.kernel.org; Linuxarm
> <linuxarm at huawei.com>; xuwei (O) <xuwei5 at huawei.com>; Zengtao (B)
> <prime.zeng at hisilicon.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