Re: [PATCH RESEND 0/3] Represent cluster topology and enable load balance between clusters

From: Barry Song <21cnbao@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@redhat.com>,
	Aubrey Li <aubrey.li@linux.intel.com>,
	Borislav Petkov <bp@alien8.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Ben Segall <bsegall@google.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Guodong Xu <guodong.xu@linaro.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Jonathan Cameron <jonathan.cameron@huawei.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	"Cc: Len Brown" <lenb@kernel.org>,
	ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
	LAK <linux-arm-kernel@lists.infradead.org>,
	Linuxarm <linuxarm@huawei.com>,
	Mark Rutland <mark.rutland@arm.com>, Mel Gorman <mgorman@suse.de>,
	msys.mizuma@gmail.com, "Zengtao (B)" <prime.zeng@hisilicon.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Steven Rostedt <rostedt@goodmis.org>,
	Barry Song <song.bao.hua@hisilicon.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Will Deacon <will@kernel.org>, x86 <x86@kernel.org>,
	yangyicong <yangyicong@huawei.com>
Subject: Re: [PATCH RESEND 0/3] Represent cluster topology and enable load balance between clusters
Date: Tue, 5 Oct 2021 22:15:39 +1300	[thread overview]
Message-ID: <CAGsJ_4xZD0sG0Df666f0bvHOzuPMjnw0dN_mArER5k1pJ6LPLw@mail.gmail.com> (raw)
In-Reply-To: <20211005075001.GJ4323@worktop.programming.kicks-ass.net>

On Tue, Oct 5, 2021 at 8:50 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, Oct 01, 2021 at 04:22:46PM -0700, Tim Chen wrote:
> > On Fri, 2021-10-01 at 16:57 +0200, Peter Zijlstra wrote:
>
> > > The one questino I have is, do we want default y?
> >
> > I also agree that default y is preferable.
>
> I'll change at least the x86 one to:
>
>         default y
>         depends on SMP
>
> > > The one nit I have is the Kconfig text, I'm not really sure that's
> > > clarifying what a cluster is.
> >
> > Do you have a preference of a different name other than cluster?
> > Or simply better documentation on what a cluster is for ARM64
> > and x86 in Kconfig?
>
> Yes, better wording as to what a cluster is. Currently the x86 and arm64
> ones actually differ:
>
> x86:
>         help
>          Cluster scheduler support improves the CPU scheduler's decision
>          making when dealing with machines that have clusters of CPUs
>          sharing L2 cache. If unsure say N here.
>
> arm64:
>         help
>           Cluster scheduler support improves the CPU scheduler's decision
>           making when dealing with machines that have clusters(sharing internal
>           bus or sharing LLC cache tag). If unsure say N here.
>
>
> (also, all this stuff being replicated across arch/*/Kconfig seems
> unfortunate)

perhaps worth a separate patchset to do some cleanup so that SCHED_MC,
SCHED_SMT etc
won't be replicated in different architectures. Right now, this kind
of Kconfig option is copied
everywhere. I am seeing SCHED_SMT in all of
arch/arm/Kconfig
arch/arm64/Kconfig
arch/ia64/Kconfig
arch/mips/Kconfig
arch/powerpc/Kconfig
arch/s390/Kconfig
arch/sparc/Kconfig
arch/x86/Kconfig
...

Is it a better way to move them to a common Kconfig and let the architectures to
declare things like ARCH_HAVE_SMT?

Thanks
Barry