Re: [Xen-users] VGA passthrough with Xen 4.3 and xl toolstack - performance degradation resolved?

[Gordan Bobic <gordan@xxxxxxxxxx>]

On 03/12/2014 06:14 PM, David Sutton wrote:
> Gordon,
>
> On Wed, Mar 12, 2014 at 12:01 PM, Gordan Bobic <gordan@xxxxxxxxxx
> <mailto:gordan@xxxxxxxxxx>> wrote:
>
>     On 03/12/2014 03:42 PM, H. Sieger wrote:
>
>         Thanks for the reply! Good to know the old ATI patch still works
>         with
>         Xen 4.4.
>
>
>     If you are talking about the patch I think you are talking about,
>     IIRC that was a patch for primary passthrough. This side-steps some
>     of the problems of lack of reset by POST-ing the VBIOS in domU, so
>     VBIOS gets the card into a state where the driver knows what to do
>     with it.
>
> The patch I was referring to is the same one that you are talking about;
> basically passing through the card as a primary display, with access to
> the VBIOS so the card can go through POST and be in a better internal
> state for when the driver starts to use it.
Thanks for clarifying. I was also referring to a much more recent patch 
I saw floating around that adds bus reset as a means of resetting a PCI 
device when FLR or power management based resetting isn't available.
The only ATI card I ever saw survive a reboot was a HD7450. It didn't 
survive the reboot every time, but any number greater than 0 is a huge 
improvement. It still wasn't reliable enough for "production" use, and I 
needed something way more performant than a 7450 so I didn't stick with 
it for more than preliminary testing, but I always assumed that the 
reason it did better than higher end cards was because it was powered 
only from the slot, no auxiliary power input - which meant that 
resetting it via the power management trick (put it in powered off state 
and then bring it back online). It's just a guess, though.
Gordan

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