linux-kernel - Re: [PATCH v6] sched/clock: Avoid false sharing for sched_clock

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Message-ID: <215bbfca-8f63-4f86-b992-5802350055a4@intel.com>
Date: Tue, 27 Jan 2026 15:30:11 +0800
From: "Guo, Wangyang" <wangyang.guo@...el.com>
To: K Prateek Nayak <kprateek.nayak@....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>
Cc: 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 v6] sched/clock: Avoid false sharing for
 sched_clock_irqtime

On 1/27/2026 2:30 PM, K Prateek Nayak wrote:
> Hello Wangyang,
> 
> On 1/27/2026 10:11 AM, Wangyang Guo wrote:
>> --- a/kernel/sched/clock.c
>> +++ b/kernel/sched/clock.c
>> @@ -173,6 +173,7 @@ notrace static void __sched_clock_work(struct work_struct *work)
>>   			scd->tick_gtod, __gtod_offset,
>>   			scd->tick_raw,  __sched_clock_offset);
>>   
>> +	disable_sched_clock_irqtime();
> 
> We can come here with !irqtime_enabled() but this is a slowpath so I
> don't really mind calling disable_sched_clock_irqtime() unconditionally
> here. Feel free to include:
> 
> Reviewed-by: K Prateek Nayak <kprateek.nayak@....com>
> Tested-by: K Prateek Nayak <kprateek.nayak@....com>
> 
> Tested with a bunch of fake cases of sched_clock going unstable by
> hacking the kernel and the irqtime was disabled correctly in both cases
> - pre-lateinit and post-lateinit.

I think we can put irqtime_enabled check in disable_sched_lock_irqtime() 
which will benefit in both scenario:

  void disable_sched_clock_irqtime(void)
  {
-	sched_clock_irqtime = 0;
+	if (irqtime_enabled())
+		static_branch_disable(&sched_clock_irqtime);
  }

v7: 
https://lore.kernel.org/all/20260127072509.2627346-1-wangyang.guo@intel.com/