From: Andi Kleen <ak@suse.de>
To: Arjan van de Ven <arjan@linux.intel.com>
Subject: Re: [patch] Mark rdtsc as sync only for netburst, not for core2
Date: Tue, 28 Nov 2006 11:36:28 +0100
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On Tuesday 28 November 2006 11:28, Arjan van de Ven wrote:
> Hi,
> 
> On the Core2 cpus, the rdtsc instruction is not serializing (as defined
> in the architecture reference since rdtsc exists) and due to the deep
> speculation of these cores, it's possible that you can observe time go
> backwards between cores due to this speculation. Since the kernel
> already deals with this with the SYNC_RDTSC flag, the solution is
> simple, only assume that the instruction is serializing on family 15...
> 
> The price one pays for this is a slightly slower gettimeofday (by a
> dozen or two cycles), but that increase is quite small to pay for a
> really-going-forward tsc counter.

Added thanks

-Andi
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