linux-kernel - Re: [PATCH v7 4/8] powerpc/smp: Introduce CONFIG_SCHED

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Message-ID: <CAMuHMdXpFdjDJrMbK8+6aO=O8c8p68RUGe0o1Mo4PMmFLufc9w@mail.gmail.com>
Date: Tue, 14 Oct 2025 17:04:55 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>, K Prateek Nayak <kprateek.nayak@....com>, 
	Madhavan Srinivasan <maddy@...ux.ibm.com>, Michael Ellerman <mpe@...erman.id.au>, 
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	Alexander Gordeev <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Sven Schnelle <svens@...ux.ibm.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Juri Lelli <juri.lelli@...hat.com>, 
	Vincent Guittot <vincent.guittot@...aro.org>, linuxppc-dev@...ts.ozlabs.org, 
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org, 
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	Easwar Hariharan <easwar.hariharan@...ux.microsoft.com>, 
	Guo Weikang <guoweikang.kernel@...il.com>, 
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, Brian Gerst <brgerst@...il.com>, 
	Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>, Swapnil Sapkal <swapnil.sapkal@....com>, 
	"Yury Norov [NVIDIA]" <yury.norov@...il.com>, Sudeep Holla <sudeep.holla@....com>, 
	Jonathan Cameron <Jonathan.Cameron@...wei.com>, Andrea Righi <arighi@...dia.com>, 
	Yicong Yang <yangyicong@...ilicon.com>, 
	Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>, 
	Tim Chen <tim.c.chen@...ux.intel.com>, 
	Vinicius Costa Gomes <vinicius.gomes@...el.com>
Subject: Re: [PATCH v7 4/8] powerpc/smp: Introduce CONFIG_SCHED_MC to guard MC
 scheduling bits

Hi Peter,

On Tue, 14 Oct 2025 at 16:18, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, Oct 14, 2025 at 02:37:11PM +0200, Geert Uytterhoeven wrote:
> > > > > +       help
> > > > > +         Improves the CPU scheduler's decision making when dealing with
> > > > > +         MultiThreading at a cost of slightly increased overhead in some
> > > > > +         places. If unsure say N here.
> > > >
> > > > So it should default to n?
> > >
> > > That's just help text that got carried around. Many of the architectures
> > > that had default y still had this text on. I suppose we can change it if
> > > someone cares.
> >
> > Please do so.
>
> How about we remove the recommendation like so? There are many help
> things that do not have a recommendation. Mostly these options add a
> little code and the most expensive bits tend to be gated by
> static_branch() so it really shouldn't be that bit of a burden.
>
> CONFIG_SMP was the big one for the scheduler, and Ingo recently removed
> that (he did an effective unifdef CONFIG_SMP=y on the scheduler code).
>
> ---
> diff --git a/arch/Kconfig b/arch/Kconfig
> index ebe08b9186ad..3d8e2025a4ac 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -57,7 +57,7 @@ config SCHED_SMT
>         help
>           Improves the CPU scheduler's decision making when dealing with
>           MultiThreading at a cost of slightly increased overhead in some
> -         places. If unsure say N here.
> +         places.
>
>  config SCHED_CLUSTER
>         bool "Cluster scheduler support"
> @@ -77,7 +77,7 @@ config SCHED_MC
>         help
>           Multi-core scheduler support improves the CPU scheduler's decision
>           making when dealing with multi-core CPU chips at a cost of slightly
> -         increased overhead in some places. If unsure say N here.
> +         increased overhead in some places.
>
>  # Selected by HOTPLUG_CORE_SYNC_DEAD or HOTPLUG_CORE_SYNC_FULL
>  config HOTPLUG_CORE_SYNC

Thanks, LGTM!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds