linux-kernel - Re: [PATCH 06/15] tick/sched: Unify idle cputime accounting

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Message-ID: <20260119142607.GG830229@noisy.programming.kicks-ass.net>
Date: Mon, 19 Jan 2026 15:26:07 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	"Christophe Leroy (CS GROUP)" <chleroy@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Ben Segall <bsegall@...gle.com>, Boqun Feng <boqun.feng@...il.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
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	Jan Kiszka <jan.kiszka@...mens.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	Kieran Bingham <kbingham@...nel.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Mel Gorman <mgorman@...e.de>, Michael Ellerman <mpe@...erman.id.au>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Nicholas Piggin <npiggin@...il.com>,
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	Steven Rostedt <rostedt@...dmis.org>,
	Sven Schnelle <svens@...ux.ibm.com>,
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	Vincent Guittot <vincent.guittot@...aro.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Xin Zhao <jackzxcui1989@....com>, linux-pm@...r.kernel.org,
	linux-s390@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 06/15] tick/sched: Unify idle cputime accounting

On Fri, Jan 16, 2026 at 03:51:59PM +0100, Frederic Weisbecker wrote:

> +#ifdef CONFIG_NO_HZ_COMMON
> +void kcpustat_dyntick_start(void)
> +{
> +	if (!vtime_generic_enabled_this_cpu()) {
> +		vtime_dyntick_start();
> +		__this_cpu_write(kernel_cpustat.idle_dyntick, 1);
> +	}
> +}

Why don't we need to make sure steal time is up-to-date at this point?

> +void kcpustat_dyntick_stop(void)
> +{
> +	if (!vtime_generic_enabled_this_cpu()) {
> +		__this_cpu_write(kernel_cpustat.idle_dyntick, 0);
> +		vtime_dyntick_stop();
> +		steal_account_process_time(ULONG_MAX);
> +	}
> +}
> +#endif /* CONFIG_NO_HZ_COMMON */