linux-kernel - Re: [PATCH v2 3/3] cgroup/rstat: Add run

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <9515c474-366d-4692-91a7-a4c1a5fc18db@bytedance.com>
Date: Wed, 29 Jan 2025 12:48:09 +0800
From: Abel Wu <wuyun.abel@...edance.com>
To: Michal Koutný <mkoutny@...e.com>
Cc: Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
 Jonathan Corbet <corbet@....net>, Ingo Molnar <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 Thomas Gleixner <tglx@...utronix.de>, Yury Norov <yury.norov@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Bitao Hu
 <yaoma@...ux.alibaba.com>, Chen Ridong <chenridong@...wei.com>,
 "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
 "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] cgroup/rstat: Add run_delay accounting for cgroups

Hi Michal,

On 1/27/25 10:10 PM, Michal Koutný Wrote:
> Hello.
> 
> On Sat, Jan 25, 2025 at 01:25:12PM +0800, Abel Wu <wuyun.abel@...edance.com> wrote:
>> The per-task and per-cpu accounting have already been tracked by
>> t->sched_info.run_delay and rq->rq_sched_info.run_delay respectively.
>> Extends this to also include cgroups.
>>
>> The PSI indicator, "some" of cpu.pressure, loses the insight into how
>> severely that cgroup is stalled. Say 100 tasks or just 1 task that gets
>> stalled at a certain point will show no difference in "some" pressure.
>> IOW "some" is a flat value that not weighted by the severity (e.g. # of
>> tasks).
> 
> IIUC below are three examples of when "some" tasks are waiting for CPU:
> 
> a)
>    t1 |----|
>    t2 |xx--|
> 
> b)
>    t1 |----|
>    t2 |x---|
>    t3 |-x--|
> 
> c)
>    t1 |----|
>    t2 |xx--|
>    t3 |xx--|
> 
> (- means runnable on CPU, x means runnable waiting on RQ)
> 
> Which pair from a), b), c) is indistinguishable via PSI? (Or can you
> please add your illustrative example?)

PSI tracks stall times for each cpu, and

	tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0)

which turns nr_delayed_tasks[cpu] into boolean value, hence loses
insight into how severely this task group is stalled on this cpu.

Thanks,
	Abel