linux-kernel - Re: [PATCH 1/6] UML - Deal with host time going backwards

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Message-ID: <4846F577.10603@goop.org>
Date:	Wed, 04 Jun 2008 21:05:11 +0100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jeff Dike <jdike@...toit.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, Nix <nix@...eri.org.uk>,
	dhazelton@...er.net, linux-kernel@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: [PATCH 1/6] UML - Deal with host time going backwards

Jeff Dike wrote:
> On Wed, Jun 04, 2008 at 03:31:58PM +0100, Jeremy Fitzhardinge wrote:
>   
>> Shouldn't UML use a monotonic host clock for guest timekeeping?
>>     
>
> Indeed, Eric pointed out the posix timers, which I had forgotten
> about.  On the face of it, a monotonic timer should do the trick, but
> it's not obvious how to get it to behave like a monotonic
> gettimeofday...

You can either read the monotonic clock directly, or use it as a time 
source for a monotonic timer.  clock_gettime(CLOCK_MONOTONIC, &ts) will 
return the time in ns, and you can just feed that directly into the 
guest as a clocksource.

    J
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