linux-kernel - Re: [PATCH v2] sched/clock: Avoid false sharing for sched_clock

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Message-ID: <CAKfTPtDpdFuVo83ZbXFhTAbydq-5TxTAcf+JWeN8mK3nosJCQA@mail.gmail.com>
Date: Tue, 13 Jan 2026 11:14:54 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Wangyang Guo <wangyang.guo@...el.com>, K Prateek Nayak <kprateek.nayak@....com>, 
	Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, 
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Valentin Schneider <vschneid@...hat.com>, linux-kernel@...r.kernel.org, 
	Shrikanth Hegde <sshegde@...ux.ibm.com>, Benjamin Lei <benjamin.lei@...el.com>, 
	Tim Chen <tim.c.chen@...ux.intel.com>, Tianyou Li <tianyou.li@...el.com>
Subject: Re: [PATCH v2] sched/clock: Avoid false sharing for sched_clock_irqtime

On Tue, 13 Jan 2026 at 11:08, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Jan 13, 2026 at 03:48:07PM +0800, Wangyang Guo wrote:
> > Read-mostly sched_clock_irqtime may share the same cacheline with
> > frequently updated nohz struct. Mark it as __read_mostly to avoid
> > false sharing issue.
> >
>
> Is there a reason that thing can't be a static_key or so?

We tried that but disable_sched_clock_irqtime can be called in atomic
context with mark_tsc_unstable()
https://lore.kernel.org/all/174161357383.14745.8770394914047302959.tip-bot2@tip-bot2/