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Re: [Xen-devel] [PATCH] Fix clock_gettime to increment monotonically onP

To: Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Fix clock_gettime to increment monotonically onPV-domain/x86
From: John Levon <levon@xxxxxxxxxxxxxxxxx>
Date: Fri, 15 Jun 2007 13:47:13 +0100
Cc: Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Keir Fraser <keir@xxxxxxxxxxxxx>
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On Fri, Jun 15, 2007 at 01:12:21PM +0200, Jan Beulich wrote:

> An alternative to a spin lock would be to use a 64-bit variable storing the 
> raw
> nanosecond value, and use cmpxchg to check/update it. I did it this way for
> the clocksource monotonicity:

This is essentially what we've got now in Solaris. It seems like a
terrible shame not to just fix it in Xen, especially given all that
traffic from all CPUs to 'last_ret'.

regards
john

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