Re: [PATCH 07/18] sched/fair: Add push task mechanism for fair

[Chen Yu]

On Fri, Oct 09, 2026 at 04:31:40PM +0200, Vincent Guittot wrote:
> On Wed, 7 Oct 2026 at 04:59, Chen Yu <yu.c.chen@xxxxxxxxx> wrote:

[ ... ]

> > @@ -10414,6 +10441,15 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int select_flags)
> >         if (select_flags & WF_TTWU)
> >                 want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, p->cpus_ptr);
> >
> > +       /*
> > +        * Only a push triggered by cache aware scheduling will push the
> > +        * task towards its preferred LLC. Pushes for other reasons, like short
> > +        * slice task, uses the default push strategy.
> > +        */
> > +       push_cpu = -1;
> > +       if (select_flags & WF_RQ_PUSH)
> > +               push_cpu = check_pushable_cache_task(prev_cpu, p);
> 
> Is there any reason that you do'nt want to migrate the task at wakeup too ?
>

The wakeup path seems to be too fast to aggregate the tasks, so that multiple
CPUs try to migrate the task to the same LLC without synchronization - a task
bouncing issue was observed when cache-aware migration was enabled in the wakeup
path. We can double-check in the latest kernel to see if that is still the case,
and to see if we can mitigate that.

thanks,
Chenyu