linux-kernel - Re: [RFC PATCH] sched/cputime: drop local_irq_safe() in vtime_init

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Date:	Thu, 14 Apr 2016 09:07:26 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH] sched/cputime: drop local_irq_safe() in
 vtime_init_idle()

On Thu, 2016-04-14 at 14:29 +0200, Sebastian Andrzej Siewior wrote:
> A while ago vtime_init_idle() used to invoke sched_clock_cpu() and
> had
> write_seqlock_irqsave() because sched_clock_cpu() required to be
> called
> with interrupts off.
> This requirement is written before the body of the function and was
> introduced in 2010 via c676329abb2b ("sched_clock: Add local_clock()
> API
> and improve documentation"). This requirement has been dropped in
> 2013
> via ef08f0fff876 ("sched/clock: Remove local_irq_disable() from the
> clocks")
> but the body of the function still has the comment.
> 
> Now, vtime_init_idle() was converted from seqlock to seqcount via
> b7ce2277f087 ("sched/cputime: Convert vtime_seqlock to seqcount") and
> while doing so the IRQ-off region around sched_clock_cpu() was
> preserved
> while not strictly required (given the first part of this commit).
> A little later, sched_clock_cpu() was replaced with jiffies via
> ff9a9b4c4334 ("sched, time: Switch VIRT_CPU_ACCOUNTING_GEN to jiffy
> granularity").
> Based on this events I assume it is safe to drop the local_irq_safe()
> section.
> 
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> 

Acked-by: Rik van Riel <riel@...hat.com>

-- 
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