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From: Thomas Gleixner <tglx@linutronix.de>
To: Chris Friesen <cbf123@mail.usask.ca>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
	John Stultz <john.stultz@linaro.org>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	lkml <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>, Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH v2] sched/cputime: steal_account_process_tick() should return jiffies
Date: Sun, 6 Mar 2016 11:58:57 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.11.1603061158400.3686@nanos> (raw)
In-Reply-To: <56DBBDB8.40305@mail.usask.ca>

On Sat, 5 Mar 2016, Chris Friesen wrote:

> The callers of steal_account_process_tick() expect it to return
> whether a jiffy should be considered stolen or not.
> 
> Currently the return value of steal_account_process_tick() is in
> units of cputime, which vary between either jiffies or nsecs
> depending on CONFIG_VIRT_CPU_ACCOUNTING_GEN.
> 
> If cputime has nsecs granularity and there is a tiny amount of
> stolen time (a few nsecs, say) then we will consider the entire
> tick stolen and will not account the tick on user/system/idle,
> causing /proc/stats to show invalid data.
> 
> The fix is to change steal_account_process_tick() to accumulate
> the stolen time and only account it once it's worth a jiffy.
> 
> (Thanks to Frederic Weisbecker for suggestions to fix a bug in my
> first version of the patch.)
> 
> Signed-off-by: Chris Friesen <chris.friesen@windriver.com>

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

  reply	other threads:[~2016-03-06 11:00 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-04 22:59 [PATCH] " Chris Friesen
2016-03-05 10:27 ` Thomas Gleixner
2016-03-05 13:19   ` Frederic Weisbecker
2016-03-06  4:17     ` Chris Friesen
2016-03-06  5:18       ` [PATCH v2] sched/cputime: " Chris Friesen
2016-03-06 10:58         ` Thomas Gleixner [this message]
2016-03-08 12:29         ` Frederic Weisbecker
2016-03-08 13:18         ` [tip:sched/core] sched/cputime: Fix steal_account_process_tick() to always " tip-bot for Chris Friesen

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