linux-kernel - Re: [rfc, PATCH v1 1/1] hrtimers: Refactor hrtimer_clock_to_base

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Message-ID: <87pljljzig.ffs@tglx>
Date: Thu, 13 Feb 2025 22:39:03 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Cc: Anna-Maria Behnsen <anna-maria@...utronix.de>, Frederic Weisbecker
 <frederic@...nel.org>, Nathan Chancellor <nathan@...nel.org>, Nick
 Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>,
 Justin Stitt <justinstitt@...gle.com>, Andy Shevchenko
 <andriy.shevchenko@...ux.intel.com>
Subject: Re: [rfc, PATCH v1 1/1] hrtimers: Refactor
 hrtimer_clock_to_base_table initialisation

On Mon, Feb 10 2025 at 10:26, Andy Shevchenko wrote:
> Clang complains about overlapped initialisers in the
> hrtimer_clock_to_base_table definition. With `make W=1` and
> CONFIG_WERROR=y (which is default nowadays) this breaks
> the build:
>
>   CC      kernel/time/hrtimer.o
> kernel/time/hrtimer.c:124:21: error: initializer overrides prior initialization of this subobject [-Werror,-Winitializer-overrides]
>   124 |         [CLOCK_REALTIME]        = HRTIMER_BASE_REALTIME,
>
> kernel/time/hrtimer.c:122:27: note: previous initialization is here
>   122 |         [0 ... MAX_CLOCKS - 1]  = HRTIMER_MAX_CLOCK_BASES,
>
> (and similar for CLOCK_MONOTONIC, CLOCK_BOOTTIME, and CLOCK_TAI).
>
> Refactor hrtimer_clock_to_base_table initialisation to make
> the compiler happy.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>
> TBH, I don't like much this solution as it diminishes the point of that
> override to be there in the first place. I haven't found better alternatives
> as they may be too intrusive. Another one might be to remove this table,
> but in such case the replacement might add latency to some cases (although
> I haven't checked the generated code for, for example, switch-case approach).

The only place this table is used is in __hrtimer_init(), which is not a
hot-path. The four resulting comparisons are probably not even noticable.

Thanks,

        tglx