linux-kernel - Re: [PATCHv3 linux-next] hrtimer: Add notifier when clock_was

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Message-ID: <alpine.DEB.2.02.1309131628250.4089@ionos.tec.linutronix.de>
Date:	Fri, 13 Sep 2013 16:32:24 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Fan Du <fan.du@...driver.com>
cc:	David Miller <davem@...emloft.net>, herbert@...dor.hengli.com.au,
	steffen.klassert@...unet.com, dborkman@...hat.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCHv3 linux-next] hrtimer: Add notifier when clock_was_set
 was called

On Fri, 13 Sep 2013, Fan Du wrote:
> (2) What I have been bugging you around here for this long time is really the
> second
>     problem, I'm sorry I didn't make it clearly to you and others, which is
> below:
> 
>     Why using wall clock time to calculate soft/hard IPsec events when
> xfrm_state timer
>     out happens in its timeout handler? Because even if xfrm_state using
> CLOCK_BOOTTIME,
>     system wall clock time changing will surely disturb soft/hard IPsec
> events, which
>     you raised your concern about in (*a*).

No CLOCK_BOOTTIME is not affected by wall clock time changes. It's
basically CLOCK_MONOTONIC, it just keeps counting the suspend time as
well. So without a suspend/resume cycle CLOCK_MONOTONIC and
CLOCK_BOOTTIME are the same. After a suspend/resume cycle
CLOCK_BOOTTIME will be N seconds ahead of CLOCK_MONOTONIC, where N is
the number of seconds spent in suspend.

Thanks,

	tglx
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