Re: [PATCH v2] sched/clock: Avoid false sharing for sched_clock_irqtime

[Vincent Guittot]

On Tue, 13 Jan 2026 at 11:36, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Tue, Jan 13, 2026 at 11:14:54AM +0100, Vincent Guittot wrote:
> > On Tue, 13 Jan 2026 at 11:08, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > >
> > > On Tue, Jan 13, 2026 at 03:48:07PM +0800, Wangyang Guo wrote:
> > > > Read-mostly sched_clock_irqtime may share the same cacheline with
> > > > frequently updated nohz struct. Mark it as __read_mostly to avoid
> > > > false sharing issue.
> > > >
> > >
> > > Is there a reason that thing can't be a static_key or so?
> >
> > We tried that but disable_sched_clock_irqtime can be called in atomic
> > context with mark_tsc_unstable()
> > https://lore.kernel.org/all/174161357383.14745.8770394914047302959.tip-bot2@tip-bot2/
>
> Right, but if you note, that very same path has
> clear_sched_clock_stable(), and that is a static_key too.
>
> It's just that that punts by pushing it into a workqueue. So why not
> lift that workqueue and do both keys or something?

fair enough