From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [RFC] Correct/fast timestamping in apps under Xen
	[1 of 4]: Reliable TSC
Date: Fri, 09 Oct 2009 17:22:43 -0700
Message-ID: <4ACFD3D3.4000900@goop.org>
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To: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: kurt.hackel@oracle.com, Ian Pratt <Ian.Pratt@eu.citrix.com>, "Xen-Devel (E-mail)" <xen-devel@lists.xensource.com>, Tim Deegan <Tim.Deegan@citrix.com>, Keir Fraser <Keir.Fraser@eu.citrix.com>
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On 10/09/09 14:35, Dan Magenheimer wrote:
> Excellent!  This is an extremely important piece
> of the puzzle now filled in.
>
> Just for completeness, on your machine, what is
> the measurement for raw rdtsc?
>   

A naked inline rdtsc is about 30ns, so only about a factor of 3 better. 
Which is a surprisingly small improvement given that the full
gettimeofday path has ~150 instructions, including a couple of
multiplies, quite a few jumps and two "lsl" instructions for vgetcpu
(which each cost about 10ns).  rdtsc is an expensive instruction...

    J