Re: [Question] Do we need remote charging for cpu and cpuacct subsys?

[Daniel Jordan <daniel.m.jordan-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>]

+ 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-S51bK0XF4qpuJJETbFA3a0B3C2bhBk7L0E9HWUfgJXw@public.gmane.org/
> 
> more recently here,
> 
>    https://lore.kernel.org/lkml/YGxjwKbec68sCcqo-NiLfg/pYEd1N0TnZuCh8vA@public.gmane.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