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Date: Tue, 25 Aug 2020 14:24:05 +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 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. > > Out of curiosity, what's your compiler & compiler version? % gcc --version gcc (Debian 10.2.0-5) 10.2.0 % make O=... W=1 C=1 CF=-D__CHECK_ENDIAN__ -j64 > Alternatively we can make this a "proper" constant expression with the > below. It doesn't fix another static const in the same file, though that one requires DEBUG_SCHED to be enabled. Do you want me to split this fix and fix only the other case? > --- > > diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h > index 2d59ca77103e..b1331c4c48e9 100644 > --- a/include/linux/sched/topology.h > +++ b/include/linux/sched/topology.h > @@ -27,9 +27,11 @@ enum { > > /* Generate a mask of SD flags with the SDF_NEEDS_GROUPS metaflag */ > #define SD_FLAG(name, mflags) (name * !!((mflags) & SDF_NEEDS_GROUPS)) | > -static const unsigned int SD_DEGENERATE_GROUPS_MASK = > +enum { > + SD_DEGENERATE_GROUPS_MASK = > #include <linux/sched/sd_flags.h> > -0; > +0 > +}; > #undef SD_FLAG > > #ifdef CONFIG_SCHED_DEBUG -- With Best Regards, Andy Shevchenko
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