Re: [PATCH v3] sched/clock: Avoid false sharing for sched_clock_irqtime

[Guo, Wangyang]

On 1/24/2026 12:48 AM, K Prateek Nayak wrote:
> Hello Vincent,
>
> On 1/23/2026 9:28 PM, Vincent Guittot wrote:
> > > If TSC / any potentially unstable clock is marked unstable before
> > > sched_clock_init_late(), we never flip __sched_clock_stable.
> > >
> > > On x86 side, since we already start using TSC for native_sched_clock()
> > > super early, we have defensive measures (and a __use_tsc static key on
> > > the x86 side too) to switch the sched clock back to jiffies if we
> > > realise TSC was unstable before we hit sched_clock_init_late().
> > >
> > > This is necessary since post the sched_clock_init(),
> > > "sched_clock_running" is true and the local clocks will always uses
> > > sched_clock_noinstr() and it must be switch to jiffies on the x86 side
> > > since arch defines it.
> >
> > sched_clock_init_late() is always called so can't we check if
> > irqtime_enabled and clock is unstable then we disable irqtime
> > accounting
>
> That can be done, yes.
>
> Wangyang, can you also consolidate the irqtime disable bits (TSC and
> generic) to trigger at sched_clock_init_late() if the clock was found
> unstable and in __sched_clock_work()?
>
> Both context can directly do a static_branch_disable() without
> needing an extra delayed work.

Thanks for the advise, v4 sent out, please help to review:
https://lore.kernel.org/all/20260126021401.1490163-1-wangyang.guo@xxxxxxxxx/

BR
Wangyang