Re: [PATCH v2 3/3] cgroup: Implement cgroup2 basic CPU usage accounting

[Waiman Long]

On 08/29/2017 01:43 PM, Tejun Heo wrote:
> In cgroup1, while cpuacct isn't actually controlling any resources, it
> is a separate controller due to combination of two factors -
> 1. enabling cpu controller has significant side effects, and 2. we
> have to pick one of the hierarchies to account CPU usages on.  cpuacct
> controller is effectively used to designate a hierarchy to track CPU
> usages on.
>
> cgroup2's unified hierarchy removes the second reason and we can
> account basic CPU usages by default.  While we can use cpuacct for
> this purpose, both its interface and implementation leave a lot to be
> desired - it collects and exposes two sources of truth which don't
> agree with each other and some of the exposed statistics don't make
> much sense.  Also, it propagates all the way up the hierarchy on each
> accounting event which is unnecessary.
>
> This patch adds basic resource accounting mechanism to cgroup2's
> unified hierarchy and accounts CPU usages using it.
>
> * All accountings are done per-cpu and don't propagate immediately.
>   It just bumps the per-cgroup per-cpu counters and links to the
>   parent's updated list if not already on it.
>
> * On a read, the per-cpu counters are collected into the global ones
>   and then propagated upwards.  Only the per-cpu counters which have
>   changed since the last read are propagated.
>
> * CPU usage stats are collected and shown in "cgroup.stat" with "cpu."
>   prefix.  Total usage is collected from scheduling events.  User/sys
>   breakdown is sourced from tick sampling and adjusted to the usage
>   using cputime_adjust().
>
> This keeps the accounting side hot path O(1) and per-cpu and the read
> side O(nr_updated_since_last_read).
>
> v2: Minor changes and documentation updates as suggested by Waiman and
>     Roman.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Li Zefan <lizefan@xxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Waiman Long <waiman.long@xxxxxxx>

I just noticed that you have used my obsoleted email address in the cc
line. Would you mind changing it to the one that I am currently using?

Thanks,
Longman