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

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Message-ID: <20250716145439.GA54289@cmpxchg.org>
Date: Wed, 16 Jul 2025 10:54:39 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Beata Michalska <beata.michalska@....com>, Chris Mason <clm@...a.com>,
	mingo@...hat.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
Subject: Re: [PATCH v2 01/12] sched/psi: Optimize psi_group_change()
 cpu_clock() usage

On Wed, Jul 16, 2025 at 12:40:50PM +0200, 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>

Argh, missed that during the review as well.

Acked-by: Johannes Weiner <hannes@...xchg.org>