linux-kernel - Re: [PATCH v2 1/2] smp: Introduce a helper function to check for pending IPIs

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Message-ID: <CAPDyKFrY5kOsoOH-mcWFiaiggV4q84xOtiKHdNN4bMfFmYOQPQ@mail.gmail.com>
Date: Tue, 21 Oct 2025 12:08:02 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Ben Horgan <ben.horgan@....com>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Mark Rutland <mark.rutland@....com>, Marc Zyngier <maz@...nel.org>, 
	Maulik Shah <quic_mkshah@...cinc.com>, Sudeep Holla <sudeep.holla@....com>, 
	Daniel Lezcano <daniel.lezcano@...aro.org>, Vincent Guittot <vincent.guittot@...aro.org>, 
	linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] smp: Introduce a helper function to check for
 pending IPIs

On Mon, 20 Oct 2025 at 21:11, Ben Horgan <ben.horgan@....com> wrote:
>
> Hi Ulf,
>
> Only a comment on the naming rather than a full review.
>
> On 10/20/25 15:17, Ulf Hansson wrote:
> > When governors used during cpuidle, tries to find the most optimal
> > idlestate for a CPU or a group of CPUs, they are known to quite often fail.
> > One reason for this, is that we are not taking into account whether there
> > has been an IPI scheduled for any of the CPUs that are affected by the
> > selected idlestate.
> >
> > To enable pending IPIs to be taken into account for cpuidle decisions,
> > let's introduce a new helper function, cpus_may_have_pending_ipi().
>
> To me, "may" indicates permission, i.e. is allowed, rather than
> correctness. Would "likely" be better here, cpus_likely_have_pending_ipi()?

Sure, that sounds better to me too.

I leave it a few days to allow people to provide their additional
input, before posting a new version with the new name of the function.

>
> >
> > Note that, the implementation is intentionally as lightweight as possible,
> > in favor of always providing the correct information. For cpuidle decisions
> > this is good enough.
> >
> > Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> > Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> > ---
> >
> > Changes in v2:
> >       - Implemented a common function, rather than making it arch-specific. As
> >       suggested by Thomas and Marc.
> >       - Renamed the function to indicate that it doesn't provide correctness.
> >       - Clarified function description and commit message.
> >
> --
> Thanks,
>
> Ben
>

Kind regards
Uffe