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

From: "Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>
To: Peter Zijlstra <peterz@infradead.org>,
	Valentin Schneider <valentin.schneider@arm.com>
Cc: "catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"will@kernel.org" <will@kernel.org>,
	"rjw@rjwysocki.net" <rjw@rjwysocki.net>,
	"lenb@kernel.org" <lenb@kernel.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	Jonathan Cameron <jonathan.cameron@huawei.com>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"juri.lelli@redhat.com" <juri.lelli@redhat.com>,
	"vincent.guittot@linaro.org" <vincent.guittot@linaro.org>,
	"dietmar.eggemann@arm.com" <dietmar.eggemann@arm.com>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>,
	"bsegall@google.com" <bsegall@google.com>,
	"mgorman@suse.de" <mgorman@suse.de>,
	"mark.rutland@arm.com" <mark.rutland@arm.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	Linuxarm <linuxarm@huawei.com>, "xuwei (O)" <xuwei5@huawei.com>,
	"Zengtao (B)" <prime.zeng@hisilicon.com>
Subject: RE: [RFC PATCH v2 2/2] scheduler: add scheduler level for clusters
Date: Thu, 3 Dec 2020 09:57:09 +0000	[thread overview]
Message-ID: <ebc9da1f1fdf45479651906edbfc55a6@hisilicon.com> (raw)
In-Reply-To: <20201203092831.GH2414@hirez.programming.kicks-ass.net>

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