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

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Message-ID: <87tuhvlhae.mognet@arm.com>
Date:   Tue, 05 Oct 2021 14:42:17 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Barry Song <21cnbao@...il.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Ben Segall <bsegall@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guodong Xu <guodong.xu@...aro.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        "Cc\: Len Brown" <lenb@...nel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        LAK <linux-arm-kernel@...ts.infradead.org>,
        Linuxarm <linuxarm@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        Mel Gorman <mgorman@...e.de>, msys.mizuma@...il.com,
        "Zengtao \(B\)" <prime.zeng@...ilicon.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Will Deacon <will@...nel.org>, x86 <x86@...nel.org>,
        yangyicong <yangyicong@...wei.com>
Subject: Re: [PATCH RESEND 0/3] Represent cluster topology and enable load balance between clusters

On 05/10/21 09:50, Peter Zijlstra 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
>

Huh, so the arm64 SCHED_{SMT,MC} configs are defaultless (I added SCHED_SMT
to arm64's defconfig not so long ago), but x86 has them default y, which
I'm thinking is a tad better, and would be nice to harmonize. Unfortunately
different architectures have their own dependency requirements - arm has
ARM_CPU_TOPOLOGY, parisc has PARISC_CPU_TOPOLOGY...

Would you hate making SCHED_* a "generic" config, with a common default and
help text, and punt the arch specific stuff to an ARCH_SUPPORTS_* knob?

Something like:

arch/arm/Kconfig:
  select ARCH_SUPPORTS_SCHED_MC if ARM_CPU_TOPOLOGY

init/Kconfig:
  config SCHED_MC
    def_bool y
    depends on ARCH_SUPPORTS_SCHED_MC && SMP