linux-kernel - Re: [External] Re: [PATCH] cgroup/rstat: record the cumulative per-cpu time of cgroup and its descendants

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Message-ID: <ZMrNHf2tg8AZ2F0z@slm.duckdns.org>
Date:   Wed, 2 Aug 2023 11:39:41 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Hao Jia <jiahao.os@...edance.com>
Cc:     lizefan.x@...edance.com, hannes@...xchg.org, mkoutny@...e.com,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH] cgroup/rstat: record the cumulative
 per-cpu time of cgroup and its descendants

Hello,

On Thu, Jul 27, 2023 at 07:44:28AM -1000, Tejun Heo wrote:
> Oh yeah, I do. I'm just thinking whether we also want to expose that in the
> cgroupfs. We are currently not showing anything per-cpu and the output
> formatting gets nasty with a huge number of CPUs, so maybe that's not going
> to work out all that well. Anyways, I'll get back to you next week.

I couldn't come up with an answer. Let's go ahead with adding the field but
can you please do the followings?

* Name it to something like subtree_bstat instead of cumul_bstat. The
  counters are all cumulative.

* Are you sure the upward propagation logic is correct? It's calculating
  global delta and then propagating to the per-cpu delta of the parent. Is
  that correct because the two delta calculations always end up the same?

* Please add a comment explaining that the field is not currently used
  outside of being read from bpf / drgn and what not and that we're still
  trying to determine how to expose that in the cgroupfs interface.

Thanks.

-- 
tejun