linux-kernel - Re: [PATCH v9 1/2] sched: Fix cgroup irq time for CONFIG_IRQ_TIME

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

Message-ID: <2e3mby62lswkw454sq4b4wnjmcr6etoug5bazafutb6dbbpozl@juhpci6ebev2>
Date: Tue, 27 May 2025 17:33:41 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Yafang Shao <laoar.shao@...il.com>
Cc: mingo@...hat.com, peterz@...radead.org, hannes@...xchg.org, 
	juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com, 
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com, 
	surenb@...gle.com, linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, 
	lkp@...el.com
Subject: Re: [PATCH v9 1/2] sched: Fix cgroup irq time for
 CONFIG_IRQ_TIME_ACCOUNTING

Hello.

On Sun, May 11, 2025 at 11:07:59AM +0800, Yafang Shao <laoar.shao@...il.com> wrote:
> The CPU usage of the cgroup is relatively low at around 55%, but this usage
> doesn't increase, even with more netperf tasks. The reason is that CPU0 is
> at 100% utilization, as confirmed by mpstat:
> 
>   02:56:22 PM  CPU    %usr   %nice    %sys %iowait    %irq   %soft  %steal  %guest  %gnice   %idle
>   02:56:23 PM    0    0.99    0.00   55.45    0.00    0.99   42.57    0.00    0.00    0.00    0.00
> 
>   02:56:23 PM  CPU    %usr   %nice    %sys %iowait    %irq   %soft  %steal  %guest  %gnice   %idle
>   02:56:24 PM    0    2.00    0.00   55.00    0.00    0.00   43.00    0.00    0.00    0.00    0.00
> 
> It is clear that the %soft is excluded in the cgroup of the interrupted
> task. This behavior is unexpected. We should include IRQ time in the
> cgroup to reflect the pressure the group is under.

I think this would go against intention of CONFIG_IRQ_TIME_ACCOUNTING
(someony more familiar may chime in).

> After a thorough analysis, I discovered that this change in behavior is due
> to commit 305e6835e055 ("sched: Do not account irq time to current task"),
> which altered whether IRQ time should be charged to the interrupted task.
> While I agree that a task should not be penalized by random interrupts, the
> task itself cannot progress while interrupted. Therefore, the interrupted
> time should be reported to the user.
> 
> The system metric in cpuacct.stat is crucial in indicating whether a
> container is under heavy system pressure, including IRQ/softirq activity.
> Hence, IRQ/softirq time should be included in the cpuacct system usage,
> which also applies to cgroup2’s rstat.

So I guess, it'd be better to add a separate entry in cpu.stat with
irq_usec (instead of bundling it into system_usec in spite of
CONFIG_IRQ_TIME_ACCOUNTING).

I admit, I'd be happier if irq.pressure values could be used for
that. Maybe not the PSI ratio itself but irq.pressure:total should be
that amount. WDYT?

Michal

Download attachment "signature.asc" of type "application/pgp-signature" (229 bytes)