From: Peter Zijlstra <peterz@infradead.org>
To: Philipp Klocke <Phil_K97@gmx.de>
Cc: sil2review@lists.osadl.org, kernelnewbies@kernelnewbies.org,
llvmlinux@lists.linuxfoundation.org,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
der.herr@hofr.at, lukas.bulwahn@gmail.com
Subject: Re: [PATCH] sched/fair: Change sched_feat(x) in !CONFIG_SCHED_DEBUG case
Date: Fri, 20 Apr 2018 09:57:17 +0200 [thread overview]
Message-ID: <20180420075717.GB4064@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180416085426.24157-1-Phil_K97@gmx.de>
On Mon, Apr 16, 2018 at 10:54:26AM +0200, Philipp Klocke wrote:
> This patch is motivated by the clang warning Wconstant-logical-operand,
> issued when logically comparing a variable to a constant integer that is
> neither 1 nor 0. It happens for sched_feat(x) when sysctl_sched_features
> is constant, i.e., CONFIG_SCHED_DEBUG is not set.
>
> kernel/sched/fair.c:3927:14: warning: use of logical '&&' with constant operand [-Wconstant-logical-operand]
> if (initial && sched_feat(START_DEBIT))
> ^ ~~~~~~~~~~~~~~~~~~~~~~~
> kernel/sched/fair.c:3927:14: note: use '&' for a bitwise operation
> if (initial && sched_feat(START_DEBIT))
> ^~
> &
> kernel/sched/fair.c:3927:14: note: remove constant to silence this warning
> if (initial && sched_feat(START_DEBIT))
> ~^~~~~~~~~~~~~~~~~~~~~~~~~~
> @@ -1305,7 +1305,11 @@ static const_debug __maybe_unused unsigned int sysctl_sched_features =
> 0;
> #undef SCHED_FEAT
>
> +#ifdef CONFIG_SCHED_DEBUG
> #define sched_feat(x) (sysctl_sched_features & (1UL << __SCHED_FEAT_##x))
> +#else
> +#define sched_feat(x) ((sysctl_sched_features >> __SCHED_FEAT_##x) & 1UL)
> +#endif
So this is extra ugly, for no gain?
WTH does clang complain about a constant? Can't you just disable that
stupid warning?
Also, if sysctl_sched_features is a constant, the both expressions
_should_ really result in a constant and clang should still warn about
it.
I'm really not seeing why we'd want to do this. Just fix clang to not be
stupid.
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WARNING: multiple messages have this Message-ID (diff)
From: peterz@infradead.org (Peter Zijlstra)
To: kernelnewbies@lists.kernelnewbies.org
Subject: [PATCH] sched/fair: Change sched_feat(x) in !CONFIG_SCHED_DEBUG case
Date: Fri, 20 Apr 2018 09:57:17 +0200 [thread overview]
Message-ID: <20180420075717.GB4064@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180416085426.24157-1-Phil_K97@gmx.de>
On Mon, Apr 16, 2018 at 10:54:26AM +0200, Philipp Klocke wrote:
> This patch is motivated by the clang warning Wconstant-logical-operand,
> issued when logically comparing a variable to a constant integer that is
> neither 1 nor 0. It happens for sched_feat(x) when sysctl_sched_features
> is constant, i.e., CONFIG_SCHED_DEBUG is not set.
>
> kernel/sched/fair.c:3927:14: warning: use of logical '&&' with constant operand [-Wconstant-logical-operand]
> if (initial && sched_feat(START_DEBIT))
> ^ ~~~~~~~~~~~~~~~~~~~~~~~
> kernel/sched/fair.c:3927:14: note: use '&' for a bitwise operation
> if (initial && sched_feat(START_DEBIT))
> ^~
> &
> kernel/sched/fair.c:3927:14: note: remove constant to silence this warning
> if (initial && sched_feat(START_DEBIT))
> ~^~~~~~~~~~~~~~~~~~~~~~~~~~
> @@ -1305,7 +1305,11 @@ static const_debug __maybe_unused unsigned int sysctl_sched_features =
> 0;
> #undef SCHED_FEAT
>
> +#ifdef CONFIG_SCHED_DEBUG
> #define sched_feat(x) (sysctl_sched_features & (1UL << __SCHED_FEAT_##x))
> +#else
> +#define sched_feat(x) ((sysctl_sched_features >> __SCHED_FEAT_##x) & 1UL)
> +#endif
So this is extra ugly, for no gain?
WTH does clang complain about a constant? Can't you just disable that
stupid warning?
Also, if sysctl_sched_features is a constant, the both expressions
_should_ really result in a constant and clang should still warn about
it.
I'm really not seeing why we'd want to do this. Just fix clang to not be
stupid.
next prev parent reply other threads:[~2018-04-20 7:57 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-16 8:54 [PATCH] sched/fair: Change sched_feat(x) in !CONFIG_SCHED_DEBUG case Philipp Klocke
2018-04-18 13:49 ` Nicholas Mc Guire
2018-04-18 13:49 ` Nicholas Mc Guire
2018-04-20 7:57 ` Peter Zijlstra [this message]
2018-04-20 7:57 ` Peter Zijlstra
2018-04-20 16:29 ` Philipp Klocke
2018-04-20 16:29 ` Philipp Klocke
2018-04-20 16:51 ` Peter Zijlstra
2018-04-20 16:51 ` Peter Zijlstra
2018-04-20 21:29 ` Lukas Bulwahn
2018-04-20 21:29 ` Lukas Bulwahn
2018-04-23 9:45 ` Peter Zijlstra
2018-04-23 9:45 ` Peter Zijlstra
2018-04-20 10:34 ` Peter Zijlstra
2018-04-20 10:34 ` Peter Zijlstra
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