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Re: [Xen-devel] RE: [PATCH] rendezvous-based local time calibration WOW!

To: "dan.magenheimer@xxxxxxxxxx" <dan.magenheimer@xxxxxxxxxx>, John Levon <levon@xxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] RE: [PATCH] rendezvous-based local time calibration WOW!
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 05 Aug 2008 22:43:00 +0100
Cc: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Dave Winchell <dwinchell@xxxxxxxxxxxxxxx>
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On 5/8/08 22:27, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

>> No, as it would be incredibly slow on Solaris (I dread to imagine).
> Could be.  On my box (Conroe), trapping tsc in an hvm is faster
> than reading pit or hpet in the hypervisor or in a native OS.

For a PV guest it only punts the monotonicity problem into the hypervisor of
course. You still need to access a shared counter, or use a lock (i.e.,
communication/synchronisation between processors), or be guaranteed that
local counters (TSCs) are driven by a common clock signal with negligible

 -- Keir

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