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Date:   Fri, 2 Jul 2021 16:19:20 -0400
From:   Daniel Jordan <daniel.m.jordan@oracle.com>
To:     Hao Lee <haolee.swjtu@gmail.com>,
        Pavan Kondeti <pkondeti@codeaurora.org>,
        Wei Wang <wvw@google.com>
Cc:     linux-mm@kvack.org, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, tj@kernel.org
Subject: Re: [Question] Do we need remote charging for cpu and cpuacct subsys?
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+ 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