Re: [PATCH 8/9] sched/psi: add kernel cmdline parameter psi_inner_cgroup

[Tejun Heo <tj@kernel.org>]

Hello,

On Wed, Aug 03, 2022 at 03:22:16PM -0400, Johannes Weiner wrote:
> Where it gets trickier is also stopping the tracking of task counts in
> a cgroup. For re-enabling afterwards, we'd have to freeze scheduler
> and cgroup state and find all tasks of interest across all CPUs for
> the given cgroup to recreate the counts. I'm not quite sure whether
> that's feasible, and if so, whether it's worth the savings.

If this turns out to be necessary, I wonder whether we can just be
opportunistic. ie. don't bother with walking all the tasks but only remember
whether a task is accounted at a given level or not (this can be a bitmap
which is allocated at cgroup attach type and in most caess will be pretty
small). Then, maybe we can just start accounting them as they cycle through
state transitions - we ignore the ones leaving states that they weren't
accounted for and start remembering the new states they enter.

Thanks.

-- 
tejun