Re: [Xen-users] Difference between primary and secondary VGA pass through

[Gordan Bobic <gordan@xxxxxxxxxx>]

On 2014-05-02 11:41, Daniel Shub wrote:
> > On 2 May 2014, at 10:10, "Gordan Bobic" <gordan@xxxxxxxxxx> wrote:
> >
> > > On 2014-05-02 08:08, H. Sieger wrote:
> > > Well, I've recently gave KVM a try and saw primary passthrough 
> > > working
> > > in my setup - that was until I installed the AMD driver in Windows
> > > after which the guest didn't boot anymore/blue screen .
> > >
> > > I believe primary passthrough can shorten the boot time of the guest,
> > > but other than that I wouldn't break my head over that.
> > Primary passthrough re-POSTs and initializes the GPU via the BIOS.
> > That means you get to see the BIOS POST and OS loading screen on
> > the physical rather than emulated GPU. Other than that there is no
> > difference.
> >
> > The reason why primary passthrough was of interest recently was
> > because ATI cards/drivers didn't handle rebooting domU gracefully,
> > and re-POST-ing the card via the BIOS was a way of getting card
> > back into a usable state without be driver choking on it in various
> > ways. Now that the slot-level reset is being implemented, it makes
> > for a simpler, more generic way to reset the card, which I guess
> > takes some of the pressure for the need for primary passthrough
> > for ATI cards.
> >
> > Nvidia binary drivers handle the card initialization gracefully
> > (provided the card's device ID is in the expensive
> > Quadro/Tesla/Grid white-list - hence why a lot of us have been
> > modifying various GeForce cards into equivalent Quadros) whatever
> > state it was left in, so this was never an issue for those.
> Do the open source Linux ATI/Radeon drivers support FLR?
FLR is a _hardware_ feature, and no, no GPUs support FLR.

> When I pass
> my ATI card as a secondary device to a Linux DomU I can only get it to
> work with the proprietary Catalyst driver.
Are you a PV or HVM domU? You may have slightly better luck if it's PV.

Gordan

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