Re: [PATCH] sched/clock: Avoid false sharing for sched_clock_irqtime

[Guo, Wangyang]

On 1/13/2026 12:26 PM, K Prateek Nayak wrote:
> Hello Wangyang,
>
> On 1/13/2026 8:36 AM, Wangyang Guo wrote:
> > Read-mostly sched_clock_irqtime may share the same cacheline with
> > frequently updated nohz struct. Make it as cache aligned to avoid
> > false sharing issue.
>
> nit.
>
> Since you mention this is a "Read-mostly" data ...
>
> [..snip..]
>
> > diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> > index 7097de2c8cda..34d15972f5fb 100644
> > --- a/kernel/sched/cputime.c
> > +++ b/kernel/sched/cputime.c
> > @@ -25,7 +25,7 @@
> >    */
> >   DEFINE_PER_CPU(struct irqtime, cpu_irqtime);
> >   
> > -int sched_clock_irqtime;
> > +int sched_clock_irqtime __cacheline_aligned;
>
> Have you tried annotating it with "__ro_after_init" or "__read_mostly"?
>
> That should also ensure "sched_clock_irqtime" doesn't have false-sharing
> with the nohz struct without using an entire cacheline worth of space.

__read_mostly works and avoids wasting spaces. It's better than 
__cacheline_aligned, patch v2 is sent out as:
https://lore.kernel.org/all/20260113074807.3404180-1-wangyang.guo@xxxxxxxxx/

BR
Wangyang