linux-kernel - Re: [PATCH 6/6] selftests/mm: Don't fail uffd-stress if too many CPUs

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Message-ID: <CA+i-1C1VjdMb6YLEvORkZhiqVCE_G5BphJmAcr00U6KCfC7xtw@mail.gmail.com>
Date: Thu, 20 Feb 2025 16:55:34 +0100
From: Brendan Jackman <jackmanb@...gle.com>
To: Dev Jain <dev.jain@....com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Shuah Khan <shuah@...nel.org>, Mateusz Guzik <mjguzik@...il.com>, linux-mm@...ck.org, 
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] selftests/mm: Don't fail uffd-stress if too many CPUs

On Thu, 20 Feb 2025 at 16:48, Dev Jain <dev.jain@....com> wrote:
>
>
>
> On 20/02/25 8:33 pm, Brendan Jackman wrote:
> > This calculation divides a fixed parameter by an environment-dependent
> > parameter i.e. the number of CPUs.
> >
> > The simple way to avoid machine-specific failures here is to just put a
> > cap on the max value of the latter.
>
> I haven't read the test, but if nr_cpus is being computed, then this
> value must be important to the test somehow? Would it potentially be
> wrong to let the test run for nr_cpus != actual number of cpus?

Based on my _extremely hasty_ reading, the variable is misnamed and
it's actually a thread count not a CPU count. I can double check
that's the case and rename it.

> Also, if the patch is correct then will it be better to also print a
> diagnostic telling the user that the number of cpus is going to be
> capped for the test to run?

Sure. The level of detail in the  logging and error messages is
extremely low here so I didn't feel like being too anomalous, but why
not.