Re: [External] Re: [PATCH v2 4/4] psi: Optimize task switch inside shared cgroups

[Muchun Song]

On Wed, Mar 3, 2021 at 11:53 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Wed, Mar 03, 2021 at 11:46:59AM +0800, Chengming Zhou wrote:
> > The commit 36b238d57172 ("psi: Optimize switching tasks inside shared
> > cgroups") only update cgroups whose state actually changes during a
> > task switch only in task preempt case, not in task sleep case.
> >
> > We actually don't need to clear and set TSK_ONCPU state for common cgroups
> > of next and prev task in sleep case, that can save many psi_group_change
> > especially when most activity comes from one leaf cgroup.
> >
> > sleep before:
> > psi_dequeue()
> >   while ((group = iterate_groups(prev)))  # all ancestors
> >     psi_group_change(prev, .clear=TSK_RUNNING|TSK_ONCPU)
> > psi_task_switch()
> >   while ((group = iterate_groups(next)))  # all ancestors
> >     psi_group_change(next, .set=TSK_ONCPU)
> >
> > sleep after:
> > psi_dequeue()
> >   nop
> > psi_task_switch()
> >   while ((group = iterate_groups(next)))  # until (prev & next)
> >     psi_group_change(next, .set=TSK_ONCPU)
> >   while ((group = iterate_groups(prev)))  # all ancestors
> >     psi_group_change(prev, .clear=common?TSK_RUNNING:TSK_RUNNING|TSK_ONCPU)
> >
> > When a voluntary sleep switches to another task, we remove one call of
> > psi_group_change() for every common cgroup ancestor of the two tasks.
> >
> Co-developed-by: Muchun ?

Yes. Should Chengming send another version patch to add Co-developed-by tag?

> > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>