linux-kernel - Re: [PATCH v2 01/12] sched/psi: Optimize psi_group_change() cpu

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Message-ID: <72b7f683-0497-4fab-a05d-333ec5d2c309@amd.com>
Date: Fri, 25 Jul 2025 10:43:03 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>
CC: Chris Mason <clm@...a.com>, <juri.lelli@...hat.com>,
	<vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
	<rostedt@...dmis.org>, <bsegall@...gle.com>, <mgorman@...e.de>,
	<vschneid@...hat.com>, <linux-kernel@...r.kernel.org>, Johannes Weiner
	<hannes@...xchg.org>, Beata Michalska <beata.michalska@....com>
Subject: Re: [PATCH v2 01/12] sched/psi: Optimize psi_group_change()
 cpu_clock() usage

Hello Ingo, Peter,

On 7/16/2025 4:10 PM, Peter Zijlstra wrote:
> On Wed, Jul 16, 2025 at 08:53:01AM +0200, Beata Michalska wrote:
>> Wouldn't it be enough to use SEQCNT_ZERO? Those are static per-cpu ones.
> 
> Yeah, I suppose that should work. The below builds, but I've not yet
> observed the issue myself.
> 
> ---
> Subject: sched/psi: Fix psi_seq initialization
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Tue, 15 Jul 2025 15:11:14 -0400
> 
> With the seqcount moved out of the group into a global psi_seq,
> re-initializing the seqcount on group creation is causing seqcount
> corruption.
> 
> Fixes: 570c8efd5eb7 ("sched/psi: Optimize psi_group_change() cpu_clock() usage")
> Reported-by: Chris Mason <clm@...a.com>
> Suggested-by: Beata Michalska <beata.michalska@....com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

I've been running with this fix for a bunch of my testing and when I forget
about it (as was the case when testing John's Proxy Exec branch), I usually
run into the softlockup in psi_avgs_work().

Is it too late to include this in tip:sched/core for v6.17?

Also feel free to include:

Tested-by: K Prateek Nayak <kprateek.nayak@....com>

-- 
Thanks and Regards,
Prateek