linux-kernel - Re: [PATCH 0/2] Exposing nice CPU usage to userspace

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Message-ID: <tpqxx4hk45qkbt5e7sb3jlomfcqt5ickbor5gmclvbqxbrngp6@yqltckvwce3z>
Date: Mon, 26 Aug 2024 13:59:34 +0200
From: Michal Koutný <mkoutny@...e.com>
To: JoshuaHahnjoshua.hahn6@...il.com
Cc: tj@...nel.org, lizefan.x@...edance.com, hannes@...xchg.org, 
	shuah@...nel.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 0/2] Exposing nice CPU usage to userspace

Hello.

On Fri, Aug 23, 2024 at 01:05:16PM GMT, JoshuaHahnjoshua.hahn6@...il.com wrote:
> Niced CPU usage is a metric reported in host-level /proc/stat, but is
> not reported in cgroup-level statistics in cpu.stat. However, when a
> host contains multiple tasks across different workloads, it becomes
> difficult to gauage how much of the task is being spent on niced
> processes based on /proc/stat alone, since host-level metrics do not
> provide this cgroup-level granularity.

The difference between the two metrics is in cputime.c:
        index = (task_nice(p) > 0) ? CPUTIME_NICE : CPUTIME_USER;

> Exposing this metric will allow load balancers to correctly probe the
> niced CPU metric for each workload, and make more informed decisions
> when directing higher priority tasks.

How would this work? (E.g. if too little nice time -> reduce priority
of high prio tasks?)

Thanks,
Michal