linux-kernel - Re: [PATCH 0/2] Make the TSC safe to be used by gettimeofday().

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Message-ID: <4559F781.6020607@FreeBSD.org>
Date:	Tue, 14 Nov 2006 09:06:09 -0800
From:	Suleiman Souhlal <ssouhlal@...eBSD.org>
To:	Shem Multinymous <multinymous@...il.com>
CC:	Andi Kleen <ak@...e.de>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>,
	vojtech@...e.cz, Jiri Bohac <jbohac@...e.cz>,
	Nigel Cunningham <ncunningham@...lades.com>,
	Pavel Machek <pavel@...e.cz>
Subject: Re: [PATCH 0/2] Make the TSC safe to be used by gettimeofday().

Shem Multinymous wrote:
> On 11/14/06, Suleiman Souhlal <ssouhlal@...ebsd.org> wrote:
> 
>> I believe that the results returned will always be monotonic, as long as
>> the frequency of the TSC does not change from under us (that is, without
>> the kernel knowing). This is because we "synchronize" each CPU's vxtime
>> with a global time source (HPET) every time we know the TSC rate changes.
> 
> 
> Does this hold after a suspend/resume cycle? You could be resuming
> with a different CPU clock than what you suspended with, and I'm not
> sure anything guarantees an early enough re-sync.

I have to admit that I didn't really design this patch with 
suspend/resume in mind, and that I'm not too familiar with how they work.

Do the HPET/ACPI timers still run while the system is suspended?
If not, there shouldn't be any problem, as long as the kernel is 
informed of the resume early enough.

-- Suleiman
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