linux-kernel - Re: [PATCH] clocksource: Utilize cpumask_next

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Message-ID: <CANDhNCoJ_MmpEfyuL+JWav+NUfQDH3dm196JSE-Mv3QrPUzi3g@mail.gmail.com>
Date: Wed, 11 Jun 2025 11:35:13 -0700
From: John Stultz <jstultz@...gle.com>
To: I Hsin Cheng <richard120310@...il.com>, Yury Norov <yury.norov@...il.com>
Cc: tglx@...utronix.de, sboyd@...nel.org, linux-kernel@...r.kernel.org, 
	jserv@...s.ncku.edu.tw, skhan@...uxfoundation.org, 
	linux-kernel-mentees@...ts.linux.dev
Subject: Re: [PATCH] clocksource: Utilize cpumask_next_wrap() to shrink code size

On Wed, Jun 11, 2025 at 3:45 AM I Hsin Cheng <richard120310@...il.com> wrote:
>
> Simplify the procedure of CPU random selection under
> "clocksource_verify_choose_cpus()" with "cpumask_next_wrap()". The
> logic is still the same but with this change it can shrink the code size
> by 18 bytes and increase readability.
>
> $ ./scripts/bloat-o-meter vmlinux_old vmlinux_new
> add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-18 (-18)
> Function                                     old     new   delta
> clocksource_verify_percpu                   1064    1046     -18
>
> Signed-off-by: I Hsin Cheng <richard120310@...il.com>
> ---
>  kernel/time/clocksource.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> index bb48498ebb5a..ab580873408b 100644
> --- a/kernel/time/clocksource.c
> +++ b/kernel/time/clocksource.c
> @@ -343,9 +343,7 @@ static void clocksource_verify_choose_cpus(void)
>          */
>         for (i = 1; i < n; i++) {
>                 cpu = get_random_u32_below(nr_cpu_ids);
> -               cpu = cpumask_next(cpu - 1, cpu_online_mask);
> -               if (cpu >= nr_cpu_ids)
> -                       cpu = cpumask_first(cpu_online_mask);
> +               cpu = cpumask_next_wrap(cpu - 1, cpu_online_mask);
>                 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
>                         cpumask_set_cpu(cpu, &cpus_chosen);
>         }

I think Yury submitted the same change here recently:
  https://lore.kernel.org/lkml/20250607141106.563924-3-yury.norov@gmail.com/

Though, I think he has another iteration needed as Thomas had feedback
on the subject line.

The bloat-o-meter data is a nice inclusion here!

Yury: Would you be open to adapting I Hsin Cheng's commit message into
yours and adding them as co-author via the Co-developed-by: tag?
(Assuming I Hsin Cheng agrees - See
Documentation/process/submitting-patches.rst for how to do this
properly).

thanks
-john