linux-kernel - Re: [PATCH v7 0/8] sched/fair: Get rid of sched_domains_curr

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Message-ID: <e3e216b5-445d-4d63-a700-102f996c5e10@amd.com>
Date: Mon, 1 Sep 2025 10:09:48 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>, Valentin Schneider
	<vschneid@...hat.com>, Peter Zijlstra <peterz@...radead.org>, "Madhavan
 Srinivasan" <maddy@...ux.ibm.com>
CC: Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt
	<rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman
	<mgorman@...e.de>, <thomas.weissschuh@...utronix.de>, Li Chen
	<chenl311@...natelecom.cn>, Bibo Mao <maobibo@...ngson.cn>, Mete Durlu
	<meted@...ux.ibm.com>, Tobias Huschle <huschle@...ux.ibm.com>, "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>, Michael Ellerman <mpe@...erman.id.au>, "Nicholas
 Piggin" <npiggin@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>,
	Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
	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>
Subject: Re: [PATCH v7 0/8] sched/fair: Get rid of sched_domains_curr_level
 hack for tl->cpumask()

Hello Shrikanth,

On 8/29/2025 2:23 PM, Shrikanth Hegde wrote:
> I was looking at: https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=sched/core
> 
> Current code doesn't allow one to enable/disable SCHED_MC on ppc since it is set always in kconfig.
> Used the below patch:
> 
> I think since the config is there, it would be good to provide a option to disable. no?

I think this makes sense.

FWIW, Peter added the "select SCHED_MC" to keep it consistent with the
current behavior.

> 
> ---
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index fc0d1c19f5a1..da5b2f8d3686 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -170,9 +170,8 @@ config PPC
>      select ARCH_STACKWALK
>      select ARCH_SUPPORTS_ATOMIC_RMW
>      select ARCH_SUPPORTS_DEBUG_PAGEALLOC    if PPC_BOOK3S || PPC_8xx
> -    select ARCH_SUPPORTS_SCHED_SMT        if PPC64 && SMP
>      select ARCH_SUPPORTS_SCHED_MC        if PPC64 && SMP
> -    select SCHED_MC                if ARCH_SUPPORTS_SCHED_MC
> +    select ARCH_SUPPORTS_SCHED_SMT        if PPC64 && SMP
>      select ARCH_USE_BUILTIN_BSWAP
>      select ARCH_USE_CMPXCHG_LOCKREF        if PPC64
>      select ARCH_USE_MEMTEST
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index 68edb66c2964..458ec5bd859e 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -1706,10 +1706,12 @@ static void __init build_sched_topology(void)
>              SDTL_INIT(tl_cache_mask, powerpc_shared_cache_flags, CACHE);
>      }
>  
> +#ifdef CONFIG_SCHED_MC
>      if (has_coregroup_support()) {
>          powerpc_topology[i++] =
>              SDTL_INIT(tl_mc_mask, powerpc_shared_proc_flags, MC);
>      }
> +#endif

When I was looking at this, the whole of .*coregroup.* related bits in
smp.c can technically go behind CONFIG_SCHED_MC too but that is a much
larger cleanup and perhaps unnecessary too so this looks good.

-- 
Thanks and Regards,
Prateek