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[Xen-ia64-devel] RE: PATCH: get rid of dcr bit 63 trick

To: "Tristan Gingold" <Tristan.Gingold@xxxxxxxx>, <xen-ia64-devel@xxxxxxxxxxxxxxxxxxx>, "Williamson, Alex (Linux Kernel Dev)" <alex.williamson@xxxxxx>
Subject: [Xen-ia64-devel] RE: PATCH: get rid of dcr bit 63 trick
From: "Magenheimer, Dan (HP Labs Fort Collins)" <dan.magenheimer@xxxxxx>
Date: Fri, 12 May 2006 09:14:03 -0700
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Thread-topic: PATCH: get rid of dcr bit 63 trick
You *really* don't like that dcr bit 63 test, do you? :-)

One disadvantage of your "cpl!=0" test is that it
gives the "wrong" answer for a fully-virtualized
domain.  Arun Sharma (before he left Intel) was looking
at ways of combining paravirtualization performance
into a fully-virtualized domain.

Also, per the last time this was discussed, I think there
are plans in future Itaniums to architect the
discovery of a virtualization layer, which will
undoubtedly be different than both the dcr-bit-63 and
cpl!=0 method, so we will just have to change it again
in the future.

Dan

> -----Original Message-----
> From: Tristan Gingold [mailto:Tristan.Gingold@xxxxxxxx] 
> Sent: Friday, May 12, 2006 7:32 AM
> To: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx; Magenheimer, Dan (HP 
> Labs Fort Collins); Williamson, Alex (Linux Kernel Dev)
> Subject: PATCH: get rid of dcr bit 63 trick
> 
> Hi,
> 
> instead of testing dcr bit 63 for running_on_xen, check 
> ar.rsc.pl, which 
> cannot be paravirtualized.
> 
> Testing on Xen and without Xen.
> 
> Tristan.
> 

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