[Intel-gfx] [PATCH v2 4/5] drm/i915/execlists: Read the context-status buffer from the HWSP

[Chris Wilson]

Quoting Zhenyu Wang (2017-07-13 10:14:34)
> On 2017.07.13 10:00:25 +0100, Chris Wilson wrote:
> > The engine provides a mirror of the CSB in the HWSP. If we use the
> > cacheable reads from the HWSP, we can shave off a few mmio reads per
> > context-switch interrupt (which are quite frequent!). Just removing a
> > couple of mmio is not enough to actually reduce any latency, but a small
> > reduction in overall cpu usage.
> 
> Unfortunately current gvt's execlist emulation depends on MMIO CSB read
> for guest workload without guest HWSP update. So this can't work for guest.
> We need to fix that in gvt, also reduce MMIO trap is good benefit for vGPU too.
> But might have to fallback to mmio mode if vgpu active now, and once gvt host
> got fixed, will notify through pvinfo to enable this.

Is there any chance you can work with Tomi to get a gvt-g test host in
CI, or provide a similar CI service for gvt (would have to be coupled
into trybot as well)?

Also I will have to try to remember to cc you on any execlists/guc patches
in future.
-Chris