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

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Message-ID: <20200825113202.GX1891694@smile.fi.intel.com>
Date:   Tue, 25 Aug 2020 14:32:02 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Valentin Schneider <valentin.schneider@....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 Tue, Aug 25, 2020 at 02:26:05PM +0300, Andy Shevchenko wrote:
> On Tue, Aug 25, 2020 at 02:24:05PM +0300, Andy Shevchenko wrote:
> > On Tue, Aug 25, 2020 at 11:12:21AM +0100, Valentin Schneider wrote:
> > > On 25/08/20 10:03, Valentin Schneider wrote:
> > > > 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.
> > > 
> > > > 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.
> > > 
> > > So I see how having this as a constvar rather than a constexpr is somewhat
> > > daft (we get an instance per compilation unit), but none of my compilers
> > > seem to complain (even with W=1). AFAIA the kernelbot didn't catch any of
> > > it either.

And even without compiler or any other analyzer / bot I can 100% sure tell that
spi.c does *not* use that symbol.

-- 
With Best Regards,
Andy Shevchenko