linux-kernel - Re: [PATCH v2 1/5] lib/test_cpumask: drop cpu_possible

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Message-ID: <84564f0f7db4a58ab7cd5314685ca2413c1d7081.camel@svanheule.net>
Date:   Sun, 21 Aug 2022 15:27:56 +0200
From:   Sander Vanheule <sander@...nheule.net>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Brendan Higgins <brendan.higgins@...ux.dev>,
        David Gow <davidgow@...gle.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, kunit-dev@...glegroups.com,
        Maíra Canal <mairacanal@...eup.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] lib/test_cpumask: drop cpu_possible_mask full
 test

Hi Yury,

Replying back in plaintext, as you sent an HTML message.

On Sun, 2022-08-21 at 09:18 -0400, Yury Norov wrote:
> 
> 
> On Sun, Aug 21, 2022, 09:08 Sander Vanheule <sander@...nheule.net> wrote:
> > Hi Yury,
> > 
> > On Sat, 2022-08-20 at 14:35 -0700, Yury Norov wrote:
> > > On Sat, Aug 20, 2022 at 05:03:09PM +0200, Sander Vanheule wrote:
> > > > 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) can return false for valid system
> > > > configurations.
> > > 
> > > It doesn't mean we can just give up. You can check validity of possible
> > > cpumask like this: 
> > >         KUNIT_EXPECT_EQ(test, nr_cpu_ids, cpumask_first_zero(&mask_all))
> > >         KUNIT_EXPECT_EQ(test, NR_CPUS, cpumask_first(&mask_all))
> > 
> > Did you mean cpu_possible_mask, or mask_all?
> 
> cpu_possble_as of curse.
> 
> > For cpu_possible_mask, these tests are in test_cpumask_first(), albeit under
> > a
> > slightly different form. Together with the tests in test_cpumask_weight()
> > and
> > test_cpumask_last(), cpu_possible_mask is already one of the more
> > constrained
> > masks.
> > 
> > 
> > For mask_all, the mask is filled up with nr_cpumask_bits <= NR_CPUS. I could
> > add
> > cpumask_first(), cpumask_first_zero(), and cpumask_last() tests though.
> > 
> > More tests could be also added for cpu_all_mask, since this does have all
> > NR_CPUS bits set, but I think that belongs in a separate patch.
> > 
> > I think the extra mask_all and cpu_all_mask test are out of scope for this
> > patch, but they could be added in another patch (for 6.1).
> 
> If you think that possible mask is tested by other parts, then can you notice
> that in comments?

Sure, I'll update the commit message to note the other constraints on
cpu_possible_mask.

Best,
Sander