Re: Design session notes: GPU acceleration in Xen

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

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On Mon, Jun 17, 2024 at 09:46:29AM +0200, Roger Pau Monné wrote:
> On Sun, Jun 16, 2024 at 08:38:19PM -0400, Demi Marie Obenour wrote:
> > In both cases, the device physical
> > addresses are identical to dom0’s physical addresses.
> 
> Yes, but a PV dom0 physical address space can be very scattered.
> 
> IIRC there's an hypercall to request physically contiguous memory for
> PV, but you don't want to be using that every time you allocate a
> buffer (not sure it would support the sizes needed by the GPU
> anyway).

Indeed that isn't going to fly. In older Qubes versions we had PV
sys-net with PCI passthrough for a network card. After some uptime it
was basically impossible to restart and still have enough contagious
memory for a network driver, and there it was about _much_ smaller
buffers, like 2M or 4M. At least not without shutting down a lot more
things to free some more memory.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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