linux-kernel - Re: [PATCH] sched/fair: Prevent cpu_busy_time from exceeding actual_cpu

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]

Date: Tue, 18 Jun 2024 17:23:49 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Qais Yousef <qyousef@...alina.io>
Cc: Xuewen Yan <xuewen.yan94@...il.com>, Xuewen Yan <xuewen.yan@...soc.com>, mingo@...hat.com, 
	peterz@...radead.org, juri.lelli@...hat.com, dietmar.eggemann@....com, 
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, 
	vschneid@...hat.com, vincent.donnefort@....com, ke.wang@...soc.com, 
	linux-kernel@...r.kernel.org, christian.loehle@....com
Subject: Re: [PATCH] sched/fair: Prevent cpu_busy_time from exceeding actual_cpu_capacity

On Mon, 17 Jun 2024 at 12:53, Qais Yousef <qyousef@...alina.io> wrote:
>
> On 06/17/24 11:07, Vincent Guittot wrote:
>
> > > And should effective_cpu_util() return a value higher than
> > > get_actual_cpu_capacity()?
> >
> > I don't think we should because we want to return the effective
> > utilization not the actual compute capacity.
> > Having an utilization of the cpu or group of cpus above the actual
> > capacity or the original capacity mainly means that we will have to
> > run longer
> >
> > By capping the utilization we filter this information.
> >
> > capacity orig = 800
> > util_avg = 700
> >
> > if we cap the capacity to 400 the cpu is expected to run twice longer
> > for the same amount of work to be done
>
> Okay makes sense. Wouldn't the util be 'wrong' (to what degree will depend on
> min/max freq ratio) though?
>
> We cap with arch_scale_capacity() still, I guess we know at this stage it is
> 100% wrong if we allow returning higher values?

I think that capping utilization to max capacity generates some energy
estimation error because it filters the fact that we run longer in
some cases.