linux-kernel - Re: [RFC v2] ARM: sched_clock: update epoch

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Date:	Sat, 28 Jul 2012 01:32:50 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Colin Cross <ccross@...roid.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Barry Song <21cnbao@...il.com>,
	Vaibhav Bedia <vaibhav.bedia@...com>,
	Russell King <linux@....linux.org.uk>,
	Krzysztof Halasa <khc@...waw.pl>,
	Nicolas Pitre <nico@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC v2] ARM: sched_clock: update epoch_cyc on resume

On Wed, Jul 25, 2012 at 4:49 AM, Colin Cross <ccross@...roid.com> wrote:

> Many clocks that are used to provide sched_clock will reset during
> suspend.  If read_sched_clock returns 0 after suspend, sched_clock will
> appear to jump forward.  This patch resets cd.epoch_cyc to the current
> value of read_sched_clock during resume, which causes sched_clock() just
> after suspend to return the same value as sched_clock() just before
> suspend.
>
> In addition, during the window where epoch_ns has been updated before
> suspend, but epoch_cyc has not been updated after suspend, it is unknown
> whether the clock has reset or not, and sched_clock() could return a
> bogus value.  Add a suspended flag, and return the pre-suspend epoch_ns
> value during this period.
>
> The new behavior is triggered by calling setup_sched_clock_needs_suspend
> instead of setup_sched_clock.
>
> Signed-off-by: Colin Cross <ccross@...roid.com>

Sweet!
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij
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