linux-kernel - Re: [PATCH v1 1/5] lib/test_cpumask: drop cpu_possible

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Date:   Wed, 10 Aug 2022 18:51:13 +0800
From:   David Gow <davidgow@...gle.com>
To:     Sander Vanheule <sander@...nheule.net>
Cc:     Yury Norov <yury.norov@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Maíra Canal <mairacanal@...eup.net>
Subject: Re: [PATCH v1 1/5] lib/test_cpumask: drop cpu_possible_mask full test

On Wed, Aug 10, 2022 at 4:45 PM Sander Vanheule <sander@...nheule.net> wrote:
>
> Hi David,
>
> On Wed, 2022-08-10 at 12:06 +0800, David Gow wrote:
> > On Wed, Aug 10, 2022 at 2:09 AM Sander Vanheule <sander@...nheule.net> wrote:
> > >
> > > cpu_possible_mask is not necessarily completely filled.  That means
> > > running a check on cpumask_full() doesn't make sense, so drop the test.
> > >
> > > Fixes: c41e8866c28c ("lib/test: introduce cpumask KUnit test suite")
> > > Link: https://lore.kernel.org/lkml/346cb279-8e75-24b0-7d12-9803f2b41c73@riseup.net/
> > > Reported-by: Maíra Canal <mairacanal@...eup.net>
> > > Signed-off-by: Sander Vanheule <sander@...nheule.net>
> > > Cc: David Gow <davidgow@...gle.com>
> > > ---
> >
> > Looks good to me. It'd maybe be worth noting _why_  cpu_possible_mask
> > is not always filled (i.e., that the number of available CPUs might
> > not match the maximum number of CPUs the kernel is built to support),
> > but it's probably not worth doing a new version of the patch series
> > just for that.
> >
> > Reviewed-by: David Gow <davidgow@...gle.com>
>
> Thanks for the reviews!
>
> Perhaps the commit message could be replaced by:
>
> "When the number of CPUs that can possibly be brought online is known at boot time, e.g. when
> HOTPLUG is disabled, nr_cpu_ids may be smaller than NR_CPUS. In that case, cpu_possible_mask would
> not be completely filled, and cpumask_full(cpu_possible_mask) may return false for valid system
> configurations."
>

Sounds good to me! Thanks!

-- David