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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Fri, 26 Apr 2024 19:57:48 +0200
Message-ID: <CAJZ5v0hBCM0a4DiK1fCnK1QCk3ABykXJQ8p-ZB5qJAh8yf5HhA@mail.gmail.com>
Subject: Re: [PATCH v8 01/16] ACPI: processor: Simplify initial onlining to
 use same path for cold and hotplug
To: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Miguel Luis <miguel.luis@oracle.com>, Thomas Gleixner <tglx@linutronix.de>, 
	Peter Zijlstra <peterz@infradead.org>, 
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>, 
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	Russell King <linux@armlinux.org.uk>, "Rafael J . Wysocki" <rafael@kernel.org>, 
	James Morse <james.morse@arm.com>, Salil Mehta <salil.mehta@huawei.com>, 
	Jean-Philippe Brucker <jean-philippe@linaro.org>, Catalin Marinas <catalin.marinas@arm.com>, 
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On Fri, Apr 26, 2024 at 7:49=E2=80=AFPM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Fri, 26 Apr 2024 17:21:41 +0000
> Miguel Luis <miguel.luis@oracle.com> wrote:
>
> > Hi Jonathan,
> >
> > > On 26 Apr 2024, at 16:05, Miguel Luis <miguel.luis@oracle.com> wrote:
> > >
> > >
> > >
> > >> On 26 Apr 2024, at 13:51, Jonathan Cameron <Jonathan.Cameron@huawei.=
com> wrote:
> > >>
> > >> Separate code paths, combined with a flag set in acpi_processor.c to
> > >> indicate a struct acpi_processor was for a hotplugged CPU ensured th=
at
> > >> per CPU data was only set up the first time that a CPU was initializ=
ed.
> > >> This appears to be unnecessary as the paths can be combined by letti=
ng
> > >> the online logic also handle any CPUs online at the time of driver l=
oad.
> > >>
> > >> Motivation for this change, beyond simplification, is that ARM64
> > >> virtual CPU HP uses the same code paths for hotplug and cold path in
> > >> acpi_processor.c so had no easy way to set the flag for hotplug only=
.
> > >> Removing this necessity will enable ARM64 vCPU HP to reuse the exist=
ing
> > >> code paths.
> > >>
> > >> Leave noisy pr_info() in place but update it to not state the CPU
> > >> was hotplugged.
> >
> > On a second thought, do we want to keep it? Can't we just assume that n=
o
> > news is good news while keeping the warn right after __acpi_processor_s=
tart ?
>
> Good question - my inclination was to keep this in place for now as remov=
ing
> it would remove a source of information people may expect on x86 hotplug.
>
> Then maybe propose dropping it as overly noisy kernel as a follow up
> patch after this series is merged.  Felt like a potential rat hole I didn=
't
> want to go down if I could avoid it.
>
> If any x86 experts want to shout that no one cares then I'll happily drop
> the print.

You can do that I think and see if anyone complains.  I'm not really
expecting this to happen, though.