> From: Gerd Hoffmann [mailto:kraxel@redhat.com] > Sent: Thursday, November 19, 2015 4:41 PM > > Hi, > > > > Another area of extension is how to expose a framebuffer to QEMU for > > > seamless integration into a SPICE/VNC channel. For this I believe we > > > could use a new region, much like we've done to expose VGA access > > > through a vfio device file descriptor. An area within this new > > > framebuffer region could be directly mappable in QEMU while a > > > non-mappable page, at a standard location with standardized format, > > > provides a description of framebuffer and potentially even a > > > communication channel to synchronize framebuffer captures. This would > > > be new code for QEMU, but something we could share among all vGPU > > > implementations. > > > > Now GVT-g already provides an interface to decode framebuffer information, > > w/ an assumption that the framebuffer will be further composited into > > OpenGL APIs. > > Can I have a pointer to docs / code? > > iGVT-g_Setup_Guide.txt mentions a "Indirect Display Mode", but doesn't > explain how the guest framebuffer can be accessed then. You can check "fb_decoder.h". One thing to clarify. Its format is actually based on drm definition, instead of OpenGL. Sorry for that. > > > So the format is defined according to OpenGL definition. > > Does that meet SPICE requirement? > > Yes and no ;) > > Some more background: We basically have two rendering paths in qemu. > The classic one, without opengl, and a new, still emerging one, using > opengl and dma-bufs (gtk support merged for qemu 2.5, sdl2 support will > land in 2.6, spice support still WIP, hopefully 2.6 too). For best > performance you probably want use the new opengl-based rendering > whenever possible. However I do *not* expect the classic rendering path > disappear, we'll continue to need that in various cases, most prominent > one being vnc support. > > So, for non-opengl rendering qemu needs the guest framebuffer data so it > can feed it into the vnc server. The vfio framebuffer region is meant > to support this use case. what's the format requirement on that framebuffer? If you are familiar with Intel Graphics, there's a so-called tiling feature applied on frame buffer so it can't be used as a raw input to vnc server. w/o opengl you need do some conversion on CPU first. > > > Another thing to be added. Framebuffers are frequently switched in > > reality. So either Qemu needs to poll or a notification mechanism is required. > > The idea is to have qemu poll (and adapt poll rate, i.e. without vnc > client connected qemu will poll alot less frequently). > > > And since it's dynamic, having framebuffer page directly exposed in the > > new region might be tricky. We can just expose framebuffer information > > (including base, format, etc.) and let Qemu to map separately out of VFIO > > interface. > > Allocate some memory, ask gpu to blit the guest framebuffer there, i.e. > provide a snapshot of the current guest display instead of playing > mapping tricks? yes it works but better to be completed in user level. > > > And... this works fine with vGPU model since software knows all the > > detail about framebuffer. However in pass-through case, who do you expect > > to provide that information? Is it OK to introduce vGPU specific APIs in > > VFIO? > > It will only be used in the vgpu case, not for pass-though. > > We think it is better to extend the vfio interface to improve vgpu > support rather than inventing something new while vfio can satisfy 90% > of the vgpu needs already. We want avoid vendor-specific extensions > though, the vgpu extension should work across vendors. it's fine, as long as vgpu specific interface is allowed. :-) > > > Now there is no standard. We expose vGPU life-cycle mgmt. APIs through > > sysfs (under i915 node), which is very Intel specific. In reality different > > vendors have quite different capabilities for their own vGPUs, so not sure > > how standard we can define such a mechanism. > > Agree when it comes to create vGPU instances. > > > But this code should be > > minor to be maintained in libvirt. > > As far I know libvirt only needs to discover those devices. If they > look like sr/iov devices in sysfs this might work without any changes to > libvirt. > > cheers, > Gerd > {.n++%ݶw{.n+{G{ayʇڙ,jfhz_(階ݢj"mG?&~iOzv^m ?I