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

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Message-ID: <aEqFoNGGu3eOKBEL@vaxr-BM6660-BM6360>
Date: Thu, 12 Jun 2025 15:45:36 +0800
From: I Hsin Cheng <richard120310@...il.com>
To: Yury Norov <yury.norov@...il.com>
Cc: John Stultz <jstultz@...gle.com>, 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 03:04:42PM -0400, Yury Norov wrote:
> On Wed, Jun 11, 2025 at 11:35:13AM -0700, John Stultz wrote:
> > 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).
> 
> Yeah, bloat-o-meter report is good enough to add co-developed-by tag.
> I Hsin, do you agree?

Sure thing, so do I need to apply the tag myself or we'll follow Yury's
patch work?

Best regards,
I Hsin Cheng