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SubjectRe: [Question] Do we need remote charging for cpu and cpuacct subsys?
+ Android folks

On Fri, Jul 02, 2021 at 04:07:42PM -0400, Daniel Jordan wrote:
> Hello,
>
> On Fri, Jul 02, 2021 at 08:26:27AM -0000, Hao Lee wrote:
> > memcg currently has a remote charging mechanism that can charge usage to other
> > memcg instead of the one the task belongs to.
> >
> > In our environment, we need to account the cpu usage consumed by some kworkers
> > to a specific cgroup. Thus, we want to introduce a remote-charging mechanism to
> > cpu and cpuacct subsys in our kernel.
>
> I also want to see this upstream, and am actually working on it right
> now, have been for some time.
>
> So far, this is needed to properly account multithreaded padata jobs,
> memory reclaim, and net rx. Android folks have raised this issue in the
> past too, though I'm not aware of the specific kthreads that are giving
> them problems.

Pavan, Wei, do you have any details about this?

> So naturally, I'm curious about your use case and how it may be
> different from these others. What kworkers would you like to account?
>
> > I want to know if the community has a plan to do this?
> > What will the community approach look like?
>
> There has been discussion about this here,
>
> https://lore.kernel.org/lkml/20200219214112.4kt573kyzbvmbvn3@ca-dmjordan1.us.oracle.com/
>
> more recently here,
>
> https://lore.kernel.org/lkml/YGxjwKbec68sCcqo@slm.duckdns.org/
>
> and we may talk about it at LPC:
>
> https://www.linuxplumbersconf.org/event/11/page/104-accepted-microconferences#cont-perform
>
> > I think we need to move the active_memcg to a separated active_cgroup struct,
> > and the latter will contain active_memcg, active_tg, and active_cpuacct.
>
> I'm not seeing how that could work for cases that don't know the cgroup
> when the remote charging period begins. The only one I'm aware of
> that's like that is net rx, where the work to process packets has to
> start before their ultimate destination, and therefore cgroup, is known.
>
> thanks,
> Daniel

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