Re: [Qemu-devel] [RFC v2 11/12] Add virtio-gpu vhost-user backend

["Marc-André Lureau" <marcandre.lureau@gmail.com>]

On Fri, Jun 8, 2018 at 7:25 PM, Marc-André Lureau
<marcandre.lureau@gmail.com> wrote:
> Hi
>
> On Mon, Jun 4, 2018 at 11:37 AM, Gerd Hoffmann <kraxel@redhat.com> wrote:
>> On Fri, Jun 01, 2018 at 06:27:48PM +0200, Marc-André Lureau wrote:
>>> Add to virtio-gpu devices a "vhost-user" property. When set, the
>>> associated vhost-user backend is used to handle the virtio rings.
>>>
>>> For now, a socketpair is created for the backend to share the rendering
>>> results with qemu via a simple VHOST_GPU protocol.
>>
>> Why this isn't a separate device, like vhost-user-input-pci?
>
> Ok, let's have vhost-user-gpu-pci and vhost-user-vga, inheriting from
> existing devices.
>
>>> +typedef struct VhostGpuUpdate {
>>> +    uint32_t scanout_id;
>>> +    uint32_t x;
>>> +    uint32_t y;
>>> +    uint32_t width;
>>> +    uint32_t height;
>>> +    uint8_t data[];
>>> +} QEMU_PACKED VhostGpuUpdate;
>>
>> Hmm, when designing a new protocol I think we can do better than just
>> squeering the pixels into a tcp stream.  Use shared memory instead?  Due
>> to vhost we are limited to linux anyway, so we might even consider stuff
>> like dmabufs here.
>
> Well, my goal is not to invent a new spice or wayland protocol :) I
> don't care much about 2d performance at this point, more about 3d. Can
> we leave 2d improvements for another day? Beside, what would dmabuf
> bring us for 2d compared to shmem?
>
> There seems to be a lot of overhead with the roundtrip vhost-user ->
> qemu -> spice worker -> spice client -> wayland/x11 -> gpu already
> (but this isn't necessarily so bad at 60fps or less).
> Ideally, I would like to bypass qemu & spice for local rendering, but
> I don't think wayland support that kind of nested window composition
> (at least tracking messages weston --nested doesn't show that kind of
> optimization).
>
> FWIW, here are some Unigine Heaven 4.0 benchmarks (probably within +-10%):
>
> qemu-gtk/egl+virtio-gpu: fps:2.6/ score: 64
> qemu-gtk/egl+vhost-user-gpu: fps:12.9 / score: 329
>
> spice+virtio-gpu: fps:2.8 / score: 70
> spice+vhost-user-gpu: fps:12.1 / score: 304
>
> That should give an extra motivation :)
>

(host is fps:31.1 / score:784



-- 
Marc-André Lureau