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

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Message-ID: <fea6da1d-85d6-459d-9ac3-661d5909420b@ateme.com>
Date: Fri, 23 May 2025 12:24:13 +0000
From: Jean-Baptiste Roquefere <jb.roquefere@...me.com>
To: Vincent Guittot <vincent.guittot@...aro.org>
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

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*/

Thanks for your help,

jb