linux-kernel - Re: [PATCH v3] ARM64: Dynamically allocate cpumasks and increase supported CPUs to 512

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Date: Wed, 13 Mar 2024 14:35:15 +0000
From: Sudeep Holla <sudeep.holla@....com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: "Christoph Lameter (Ampere)" <cl@...ux.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Mark Rutland <mark.rutland@....com>,
	Sudeep Holla <sudeep.holla@....com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Viresh Kumar <vireshk@...nel.org>, Will Deacon <will@...nel.org>,
	Jonathan.Cameron@...wei.com, Matteo.Carlini@....com,
	Valentin.Schneider@....com, akpm@...ux-foundation.org,
	anshuman.khandual@....com, Eric Mackay <eric.mackay@...cle.com>,
	dave.kleikamp@...cle.com, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux@...linux.org.uk, robin.murphy@....com,
	vanshikonda@...amperecomputing.com, yang@...amperecomputing.com,
	Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>
Subject: Re: [PATCH v3] ARM64: Dynamically allocate cpumasks and increase
 supported CPUs to 512

On Tue, Mar 12, 2024 at 05:55:49PM +0000, Catalin Marinas wrote:
> On Tue, Mar 12, 2024 at 10:06:06AM -0700, Christoph Lameter (Ampere) wrote:
> > On Mon, 11 Mar 2024, Christoph Lameter (Ampere) wrote:
> >
> > > This could be an issue in the ARM64 arch code itself where there maybe
> > > an assumption elsewhere that a cpumask can always store up to NR_CPU
> > > cpus and not only nr_cpu_ids as OFFSTACK does.
> > >
> > > How can I exercise the opp driver in order to recreate the problem?
> > >
> > > I assume the opp driver is ARM specific? x86 defaults to OFFSTACK so if
> > > there is an issue with OFFSTACK in opp then it should fail with kernel
> > > default configuration on that platform.
> >
> > I checked the ARM64 arch sources use of NR_CPUS and its all fine.
> >
> > Also verified in my testing logs that CONFIG_PM_OPP was set in all tests.
> >
> > No warnings in the kernel log during those tests.
> >
> > How to reproduce this?
>
> I guess you need a platform with a dts that has an "operating-points-v2"
> property. I don't have any around.
>
> Sudeep was trying to trigger this code path earlier, not sure where he
> got to.

I did try to trigger this on FVP by adding OPPs + some hacks to add dummy
clock provider to successfully probe this driver. I couldn't hit the issue
reported 🙁. It could be that with the hardware clock/regulator drivers, it
take a different path in OPP core.

--
Regards,
Sudeep