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 ?
> Signed-off-by: Muchun Song <songmuc...@bytedance.com>
> Signed-off-by: Chengming Zhou <zhouchengm...@bytedance.com>
