linux-kernel - Re: [PATCH v2 2/2] powerpc/smp: Disable steal from updating CPU capacity

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Message-ID: <aS2G6XDdGse5RYw5@linux.ibm.com>
Date: Mon, 1 Dec 2025 17:45:37 +0530
From: Srikar Dronamraju <srikar@...ux.ibm.com>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Ben Segall <bsegall@...gle.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...nel.org>, Juri Lelli <juri.lelli@...hat.com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Mel Gorman <mgorman@...e.de>, Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <vschneid@...hat.com>
Subject: Re: [PATCH v2 2/2] powerpc/smp: Disable steal from updating CPU
 capacity

* Vincent Guittot <vincent.guittot@...aro.org> [2025-11-03 09:46:26]:

> Hi Sikar,
> 
> On Wed, 29 Oct 2025 at 09:32, Srikar Dronamraju <srikar@...ux.ibm.com> wrote:
> >
> > * Vincent Guittot <vincent.guittot@...aro.org> [2025-10-29 08:43:34]:
> >
> > > Hi Srikar,
> > >
> > > On Wed, 29 Oct 2025 at 07:09, Srikar Dronamraju <srikar@...ux.ibm.com> wrote:
> > > >
> > > > In a shared LPAR with SMT enabled, it has been observed that when a CPU
> > > > experiences steal time, it can trigger task migrations between sibling
> > > > CPUs. The idle CPU pulls a runnable task from its sibling that is
> > > > impacted by steal, making the previously busy CPU go idle. This reversal
> > >
> > > IIUC, the migration is triggered by the reduced capacity case when
> > > there is 1 task on the CPU

Hi Peter, Vincent

Do you have any more inputs on this?
If not can this pulled into the scheduler code.

--
Thanks and Regards
Srikar Dronamraju