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 :-) > -Chris > > -- > Chris Wilson, Intel Open Source Technology Centre > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/intel-gfx _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/intel-gfx
