On pe, 2015-08-21 at 10:24 +0800, Zhiyuan Lv wrote:
> Hi Joonas,
>
> Thanks for the review! And my reply inline.
>
> Regards,
> -Zhiyuan
>
> On Thu, Aug 20, 2015 at 02:23:11PM +0300, Joonas Lahtinen wrote:
> > Hi,
> >
> > On to, 2015-08-20 at 17:40 +0800, Zhiyuan Lv wrote:
> > > On Thu, Aug 20, 2015 at 10:22:37AM +0100, Chris Wilson wrote:
> > > > On Thu, Aug 20, 2015 at 04:55:08PM +0800, Zhiyuan Lv wrote:
> > > > > 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 ...
> > > >
> > > > The only benefit being that the guest works no matter what the
> > > > host
> > > > does?
> > >
> > > Supporting ring buffer mode may need more work in GVT-g. When we
> > > started to
> > > enable BDW support, ring buffer mode used to work but was not
> > > well
> > > tested. And
> > > the inter-VM switch (all in ringbuffer mode) may be tricker
> > > comparing
> > > with
> > > driver context switch with "MI_SET_CONTEXT", because we need to
> > > switch ring
> > > buffer whereas driver does not. Regarding this, the EXECLIST mode
> > > looks
> > > cleaner. In order to support that, we may have to: 1, change more
> > > LRI
> > > commands
> > > to MMIO in current driver; 2, more testing/debugging of inter-VM
> > > context
> > > switch flow.
> > >
> > > Based on that, I think we should really make statement that "ring
> > > buffer mode"
> > > is not supported by GVT-g on BDW :-)
> > >
> >
> > I think just move the vpgu test even before test for GEN9 just
> > making
> > it return true on intel_vgpu_active(dev) and add a comment that
> > currently vGPU only supports execlist command submission, and then
> > add
>
> Will do. Thanks!
>
> > an error early in the init in some appropriate spot if
> > intel_vgpu_active is true but logical ring context are not
> > available
> > (which would practically mean GEN < 8).
> >
> > Does that sound OK?
>
> Ring buffer mode for Haswell with vgpu is still supported. So
> probably I have
> the check like below? Thanks!
>
Ah sorry, I missed that.
> @@ -332,6 +332,12 @@ int i915_gem_context_init(struct drm_device
> *dev)
> if (WARN_ON(dev_priv->ring[RCS].default_context))
> return 0;
>
> + if (intel_vgpu_active(dev)) {
> + if (WARN_ON(HAS_LOGICAL_RING_CONTEXTS(dev) &&
> + !i915.enable_execlist))
> + return 0;
> + }
> +
This looks fine to me. Maybe comment might be in place stating that
support is not yet implemented, but could be.
Regards, Joonas
> if (i915.enable_execlists) {
> /* NB: intentionally left blank. We will allocate our
> own
> * backing objects as we need them, thank you very
> much */
>
> >
> > Regards, Joonas
> >
> > > > -Chris
> > > >
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