Re: [Xen-devel] Xen 4.3 development update

[James Harper <james.harper@xxxxxxxxxxxxxxxx>]

> > A couple of questions:
> >
> > - Does Citrix XenServer Windows PV driver work with vanilla Xen 4.2.x? I
> remember someone complaining on the list that it doesn't work.. (but I'm
> not sure about that).
> 
> I did a quick test of the XS 6.0.2 drivers on unstable and they didn't
> work.  Didn't do any debugging, however.
> 
> > - Does GPLPV do the lazy patching for WinXP on AMD?
> 
> I highly doubt it, but you'd have to ask James Harper.
> 

GPLPV does do some TPR patching. You need to add the /PATCHTPR option to your 
boot.ini. It works for 2000 as well (and 2003 before MS stopped using TPR at 
all in sp2), if anyone cares :)

For AMD, TPR access is changed to a LOCK MOVE CR8 instruction which enables 
setting of TPR without a VMEXIT. For Intel, TPR writes are only done if it 
would change the value of TPR, and reads are always done from a cached value. I 
guess this is what you mean by 'lazy'.

I think xen itself does TPR optimisation for Intel these days so this may be 
unnecessary.

It certainly makes a big difference for XP.

James


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