Re: [PATCH v8 01/16] ACPI: processor: Simplify initial onlining to use same path for cold and hotplug

From: "Rafael J. Wysocki" <rafael@kernel.org>
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>,
	 "loongarch@lists.linux.dev" <loongarch@lists.linux.dev>,
	 "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	 "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	 "linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	 "kvmarm@lists.linux.dev" <kvmarm@lists.linux.dev>,
	"x86@kernel.org" <x86@kernel.org>,
	 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>,
	 Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Hanjun Guo <guohanjun@huawei.com>,
	 Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	 Dave Hansen <dave.hansen@linux.intel.com>,
	"linuxarm@huawei.com" <linuxarm@huawei.com>,
	 "justin.he@arm.com" <justin.he@arm.com>,
	"jianyong.wu@arm.com" <jianyong.wu@arm.com>,
	 Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Sudeep Holla <sudeep.holla@arm.com>
Subject: Re: [PATCH v8 01/16] ACPI: processor: Simplify initial onlining to use same path for cold and hotplug
Date: Fri, 26 Apr 2024 19:57:48 +0200	[thread overview]
Message-ID: <CAJZ5v0hBCM0a4DiK1fCnK1QCk3ABykXJQ8p-ZB5qJAh8yf5HhA@mail.gmail.com> (raw)
In-Reply-To: <20240426184949.0000506d@Huawei.com>

On Fri, Apr 26, 2024 at 7:49 PM 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 that
> > >> per CPU data was only set up the first time that a CPU was initialized.
> > >> This appears to be unnecessary as the paths can be combined by letting
> > >> the online logic also handle any CPUs online at the time of driver load.
> > >>
> > >> 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 existing
> > >> 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 no
> > news is good news while keeping the warn right after __acpi_processor_start ?
>
> Good question - my inclination was to keep this in place for now as removing
> 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.