Re: [PATCH 3/7] drm/i915: Always enable execlists on BDW for vgpu

Zhiyuan Lv
2015-08-20T09:02:21Z

Hi Chris,

On Thu, Aug 20, 2015 at 09:34:05AM +0100, Chris Wilson wrote:
> On Thu, Aug 20, 2015 at 03:45:20PM +0800, Zhiyuan Lv wrote:
> > Broadwell hardware supports both ring buffer mode and execlist mode.
> > When i915 runs inside a VM with Intel GVT-g, we allow execlist mode
> > only. The reason is that GVT-g does not support the dynamic mode
> > switch between ring buffer mode and execlist mode when running
> > multiple virtual machines. Consider that ring buffer mode is legacy
> > mode, it makes sense to drop it inside virtual machines.
>
> If that is the case, you should query the host as to what mode it is
> running.

Thanks for the reply! You mean we query the host mode, then tell the
guest driver inside VM, so that it could use the same mode as host
right? That might be a little complicated, and the only benefit is to
support legacy ring buffer mode ...

And GVT-g host implementation was not well tested with ring buffer mode
since it cannot start windows VM. Probably I should change the commit
message to say explicitly that ring buffer mode is not supported with
GVT-g? Thanks!

Regards,
-Zhiyuan

> -Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre