Re: [Xen-users] SOLVED - Poor Windows 2003 + GPLPV performance compared to VMWare

[James Harper <james.harper@xxxxxxxxxxxxxxxx>]

> 
> On Wed, 2012-09-19 at 13:19 +0100, Adam Goryachev wrote:
> > On 19/09/12 19:43, Adam Goryachev wrote:
> > > I've updated to SP2, and will re-test in the next few hours,
> >
> > Excellent news, the issue is completely resolved, and in fact,
> > performance is now better than vmware, and better than the old
> > original physical box pre-virtualisation. The entire task now
> > completed in 30 minutes, the previous best was 40 minutes (ie, prior to
> xen).
> 
> Excellent news!
> 
> James, since you suggested it, do you happen to know what it is about
> pre-SP2 W2K3 that is so bad? Do those versions beat on the TPR or
> something else?
> 
> (Just curious)
> 

Yes it will almost certainly be TPR access. I actually thought MS made the 
change in SP1 but maybe it was SP2 (don't know if the OP upgraded from RTM to 
sp2 or sp1 to sp2, but quite possibly I just don't remember :)

The change they made means that the TPR doesn't get touched at all anymore, so 
is much faster.

For prior versions (and XP and 2000), GPLPV can patch AMD systems to use the 
CR8 (I think) registr for TPR access which is much faster. For Intel, the best 
I could do was cache TPR so that reads were fast... it's still quite a speedup. 
I thought Xen optimised this for Intel though and my patching wasn't necessary 
anymore? Or maybe the OP is running a version of xen that doesn't have that 
feature??

James


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