RE: [PATCH v5 0/6] Deliver vGPU display refresh event to userspace

[Zhang, Tina]

> -----Original Message-----
> From: intel-gvt-dev [mailto:intel-gvt-dev-bounces@xxxxxxxxxxxxxxxxxxxxx] On
> Behalf Of kraxel@xxxxxxxxxx
> Sent: Thursday, September 5, 2019 3:49 PM
> To: Zhang, Tina <tina.zhang@xxxxxxxxx>
> Cc: kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Yuan, Hang
> <hang.yuan@xxxxxxxxx>; alex.williamson@xxxxxxxxxx; Lv, Zhiyuan
> <zhiyuan.lv@xxxxxxxxx>; intel-gvt-dev@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v5 0/6] Deliver vGPU display refresh event to userspace
> 
>   Hi,
> 
> > Option 2: QEMU provides the emulated display refresh event to the
> > vgpus provided by vendor driver. For vgpus, the display refresh event
> > can be considered as the vblank event which is leveraged by guest
> > window manager to do the plane update or mode-setting.
> 
> > People are asking if option 2 could be a better choice.
> 
> Certainly worth trying, maybe it even makes sense to implement both and
> let qemu pick one, possibly even switch them at runtime.
> 
> qemu can change the refresh rate.  vnc and sdl use that to reduce the
> refresh rate in case nobody is looking (no vnc client connected, sdl window
> minimized).  It surely makes sense to make that visible to the guest so it can
> throttle display updates too.  I'm not sure vblank is the way to go though,
> guests might run into vblank irq timeouts in case the refresh rate is very
> low ...

Indeed, low vblank rate isn't expected by guest gfx driver. It complains about the timeout error all the time, when the vblank is low. 

Currently, gvt-g provides full virtualized display model (a.k.a. not pv). And the option 2 is more like a pv solution for performance optimization, which is of course a very good proposal. Since the two options have no dependency, this patch-set limits its scope to only include option 1. Thanks.


BR,
Tina

> 
> cheers,
>   Gerd
> 
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