linux-kernel - Re: [PATCH v7] sched/clock: Avoid false sharing for sched_clock

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Message-ID: <5e001aeb-50a8-475f-bff2-6d101e15d078@amd.com>
Date: Wed, 28 Jan 2026 08:35:58 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: "Guo, Wangyang" <wangyang.guo@...el.com>, Shrikanth Hegde
	<sshegde@...ux.ibm.com>
CC: <linux-kernel@...r.kernel.org>, Benjamin Lei <benjamin.lei@...el.com>,
	"Tim Chen" <tim.c.chen@...ux.intel.com>, Tianyou Li <tianyou.li@...el.com>,
	"Ingo Molnar" <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Juri
 Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>,
	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>
Subject: Re: [PATCH v7] sched/clock: Avoid false sharing for
 sched_clock_irqtime

On 1/28/2026 7:49 AM, Guo, Wangyang wrote:
> Yes, when clock mark unstable through tsc_.*mark_unstable() with non-native_sched_clock, clear_sched_clock_stable won't be called, thus sched_clock_irqtime still keep enabled.
> 
> Maybe the dedicated workqueue for sched_clock_irqtime is still needed considering this case.

In that case, shouldn't tsc_init() only enable irqtime when
using_native_sched_clock()? How can tsc_init() make a call on irqtime if
TSC isn't being used as the sched_clock() ultimately?

For kvmclock, if PVCLOCK_TSC_STABLE_BIT is not set, it'll call
clear_sched_clock_stable() at kvm_sched_clock_init() but none of the
other clocksources do so we can assume once we override the sched_clock()
it is up to the sched_clock() provider to deal with the clock stability.

-- 
Thanks and Regards,
Prateek