Re: [PATCH v2 1/7] sched/fair: Fix zero_vruntime tracking

[Peter Zijlstra]

On Mon, Mar 30, 2026 at 12:40:45PM -0700, John Stultz wrote:
> On Mon, Mar 30, 2026 at 3:10 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > This means, that if the two tasks playing leapfrog can reach the
> > critical speed to reach the overflow point inside one tick's worth of
> > time, we're up a creek.
> >
> > If this is indeed the case, then the below should cure things.
> >
> > This also means that running a HZ=100 config will increase the chances
> > of hitting this vs HZ=1000.
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 9298f49f842c..c7daaf941b26 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -9307,6 +9307,7 @@ static void yield_task_fair(struct rq *rq)
> >         if (entity_eligible(cfs_rq, se)) {
> >                 se->vruntime = se->deadline;
> >                 se->deadline += calc_delta_fair(se->slice, se);
> > +               avg_vruntime(cfs_rq);
> >         }
> >  }
> 
> I just tested with this and similar to Prateek, I also still tripped the issue.
> 
> I'll give your new patch a spin here in a second.

Stick both on please :-) AFAICT they're both real, just not convinced
they're what you're hitting.