linux-kernel - Re: [PATCH v2 09/10] sched/psi: per-cgroup PSI stats disable/re-enable interface

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Message-ID: <5ce118b3-bf3b-d9a4-004c-a5a355984b0f@bytedance.com>
Date:   Fri, 12 Aug 2022 20:36:17 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     hannes@...xchg.org, tj@...nel.org, corbet@....net,
        surenb@...gle.com, mingo@...hat.com, peterz@...radead.org,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        songmuchun@...edance.com
Subject: Re: [PATCH v2 09/10] sched/psi: per-cgroup PSI stats
 disable/re-enable interface

On 2022/8/12 18:14, Michal Koutný wrote:
> Hello Chengming.
> 
> On Mon, Aug 08, 2022 at 07:03:40PM +0800, Chengming Zhou <zhouchengming@...edance.com> wrote:
>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
>> index dd84e34bc051..ade40506ab80 100644
>> --- a/Documentation/admin-guide/cgroup-v2.rst
>> +++ b/Documentation/admin-guide/cgroup-v2.rst
>> @@ -968,6 +968,13 @@ All cgroup core files are prefixed with "cgroup."
>>  	killing cgroups is a process directed operation, i.e. it affects
>>  	the whole thread-group.
>>  
>> +  cgroup.psi
>> +	A read-write single value file that allowed values are "0" and "1".
>> +	The default is "1".
>> +
>> +	Writing "0" to the file will disable the cgroup PSI stats accounting.
>> +	Writing "1" to the file will re-enable the cgroup PSI stats accounting.
>> +
> 
> I'd suggest explaining here explicitely, this control attribute is not
> hierarchical (i.e. PSI accounting in a cgroup does not affect accounting
> in descendants and doesn't need pass enablement via ancestors from
> root). And the purpose that it "saves" cycles (where).

Thanks for the suggestion and explanation!

Could you help take a look if there is anything to improve?


--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -968,6 +968,23 @@ All cgroup core files are prefixed with "cgroup."
        killing cgroups is a process directed operation, i.e. it affects
        the whole thread-group.

+  cgroup.pressure
+       A read-write single value file that allowed values are "0" and "1".
+       The default is "1".
+
+       Writing "0" to the file will disable the cgroup PSI accounting.
+       Writing "1" to the file will re-enable the cgroup PSI accounting.
+
+       This control attribute is not hierarchical, so disable or enable PSI
+       accounting in a cgroup does not affect PSI accounting in descendants
+       and doesn't need pass enablement via ancestors from root.
+
+       The reason this control attribute exists is that PSI accounts stalls for
+       each cgroup separately and aggregates it at each level of the hierarchy.
+       This may cause non-negligible overhead for some workloads when under
+       deep level of the hierarchy, in which case this control attribute can
+       be used to disable PSI accounting in the cgroups.
+