linux-kernel - Re: [PATCH v1] sched/topology: Make compiler happy about unused constant definitions

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Message-ID: <jhjd03fdrn3.mognet@arm.com>
Date:   Tue, 25 Aug 2020 10:03:12 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH v1] sched/topology: Make compiler happy about unused constant definitions


On 25/08/20 09:26, Andy Shevchenko wrote:
> On Mon, Aug 24, 2020 at 06:09:41PM +0100, Valentin Schneider wrote:
>> On 24/08/20 16:39, Andy Shevchenko wrote:
>> > Compilation of almost each file ends up with
>> >
>> >  In file included from .../include/linux/energy_model.h:10,
>> >                 from .../include/linux/device.h:16,
>> >                 from .../drivers/spi/spi.c:8:
>> >  .../include/linux/sched/topology.h:30:27: warning: ‘SD_DEGENERATE_GROUPS_MASK’ defined but not used [-Wunused-const-variable=]
>> >     30 | static const unsigned int SD_DEGENERATE_GROUPS_MASK =
>> >        |                           ^~~~~~~~~~~~~~~~~~~~~~~~~
>> >  ...
>> >
>> > Make compiler happy by annotating the static constants with __maybwe_unused.
>> >
>>
>> That should see some use as long as the build is for SMP. This whole region
>> is guarded by #ifdef CONFIG_SMP, so an !SMP build shouldn't trigger this.
>
> Isn't SMP is default for most of the kernel builds?
> And honestly I didn't get the purpose of this comment.
>

Sorry, that's what I get for trying to be too succinct; what I tried to say
was that SD_DEGENERATE_GROUPS_MASK should very much be used for SMP. If the
build is !SMP, it shouldn't even be defined, IOW I'm perplexed as to where
this is coming from.

>> With what config/kernel are you getting this?
>
> x86_64_defconfig from the kernel sources with some drivers added (SMP or so has
> not been touched, DEBUG_SHED was enabled once to confirm that another static
> const has same issue).

Thanks, I'll poke around this.