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

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Message-ID: <432c1980-b00f-4b07-9e24-0bec52ccb5d6@samsung.com>
Date: Wed, 13 Mar 2024 17:22:33 +0100
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Sudeep Holla <sudeep.holla@....com>, Catalin Marinas
	<catalin.marinas@....com>
Cc: "Christoph Lameter (Ampere)" <cl@...ux.com>, Mark Rutland
	<mark.rutland@....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 13.03.2024 15:35, Sudeep Holla wrote:
> 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.

I can fully reproduce this issue on Khadas VIM3 and Odroid-N2 boards. 
Both Meson A311D SoC based.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland