linux-kernel - Re: IPC drop down on AMD epyc 7702P

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Message-ID: <CAKfTPtAPPG2Xa1P9r+NQZv_VkYRic+e-qxG1ODJodPUqdry7BQ@mail.gmail.com>
Date: Mon, 26 May 2025 09:53:05 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Jean-Baptiste Roquefere <jb.roquefere@...me.com>
Cc: K Prateek Nayak <kprateek.nayak@....com>, Peter Zijlstra <peterz@...radead.org>, 
	"mingo@...nel.org" <mingo@...nel.org>, Juri Lelli <juri.lelli@...hat.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...en8.de>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, 
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	"Gautham R. Shenoy" <gautham.shenoy@....com>, Swapnil Sapkal <swapnil.sapkal@....com>, 
	Valentin Schneider <vschneid@...hat.com>, 
	"regressions@...ts.linux.dev" <regressions@...ts.linux.dev>, 
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: IPC drop down on AMD epyc 7702P

On Fri, 23 May 2025 at 14:24, Jean-Baptiste Roquefere
<jb.roquefere@...me.com> wrote:
>
> Hello Vincent,
>
> > As said previously, I don't see an obvious connection between commit
> > 16b0a7a1a0af  ("sched/fair: Ensure tasks spreading in LLC during LB")
> > which mainly ensures a better usage of CPUs inside a LLC. Do you have
> > cpufreq and freq scaling enabled ? The only link that I could think
> > of, is that the spread of task inside a llc favors inter LLC newly
> > idle load balance
> # lsmod | grep cpufreq
> cpufreq_userspace      16384  0
> cpufreq_conservative    16384  0
> cpufreq_powersave      16384  0
>
>
> but I'm not sure cpufreq is well loaded :
>
> # cpupower frequency-info
> analyzing CPU 0:
>    no or unknown cpufreq driver is active on this CPU
>    CPUs which run at the same hardware frequency: Not Available
>    CPUs which need to have their frequency coordinated by software: Not
> Available
>    maximum transition latency:  Cannot determine or is not supported.
> Not Available
>    available cpufreq governors: Not Available
>    Unable to determine current policy
>    current CPU frequency: Unable to call hardware
>    current CPU frequency:  Unable to call to kernel
>    boost state support:
>      Supported: yes
>      Active: yes
>      Boost States: 0
>      Total States: 3
>      Pstate-P0:  2000MHz
>      Pstate-P1:  1800MHz
>      Pstate-P2:  1500MHz
>
> And I cant find cpufreq/ under /sys/devices/system/cpu/cpu*/

Looks like you don't have cpufreq driver so we can forget a perf drop
because of a lower avg freq
Thanks

>
>
> Thanks for your help,
>
> jb
>