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

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Message-ID: <868b9993-34a2-4b33-b47a-989b2c680689@linux.ibm.com>
Date: Wed, 28 Jan 2026 11:56:52 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: K Prateek Nayak <kprateek.nayak@....com>,
        "Guo, Wangyang" <wangyang.guo@...el.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 1/28/26 8:35 AM, K Prateek Nayak wrote:
> 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.
> 

I think this would depend if mark_tsc_unstable happens after system boot,
specially while running kvm guest?