[Intel-gfx] [PATCH V2] drm/i915: Use I915_MAP_WC for execlists context buffer on the platforms without LLC

[Chris Wilson]

Quoting Zhao, Yakui (2018-06-22 09:06:27)
> 
> 
> >-----Original Message-----
> >From: Chris Wilson [mailto:chris at chris-wilson.co.uk]
> >Sent: Friday, June 22, 2018 3:37 PM
> >To: Zhao, Yakui <yakui.zhao at intel.com>; intel-gfx at lists.freedesktop.org
> >Subject: RE: [PATCH V2] drm/i915: Use I915_MAP_WC for execlists context
> >buffer on the platforms without LLC
> >
> >Quoting Zhao, Yakui (2018-06-22 08:29:15)
> >>
> >>
> >> >-----Original Message-----
> >> >From: Chris Wilson [mailto:chris at chris-wilson.co.uk]
> >> >Sent: Friday, June 22, 2018 2:36 PM
> >> >To: Zhao, Yakui <yakui.zhao at intel.com>;
> >> >intel-gfx at lists.freedesktop.org
> >> >Cc: Zhao, Yakui <yakui.zhao at intel.com>
> >> >Subject: Re: [PATCH V2] drm/i915: Use I915_MAP_WC for execlists
> >> >context buffer on the platforms without LLC
> >> >
> >> >Quoting Zhao Yakui (2018-06-22 07:09:10)
> >> >> @@ -2728,6 +2729,7 @@ populate_lr_context(struct i915_gem_context
> >*ctx,
> >> >>                     struct intel_engine_cs *engine,
> >> >>                     struct intel_ring *ring)  {
> >> >> +       enum i915_map_type map = HAS_LLC(ctx->i915) ? I915_MAP_WB :
> >> >> + I915_MAP_WC;
> >> >>         void *vaddr;
> >> >>         u32 *regs;
> >> >>         int ret;
> >> >> @@ -2738,13 +2740,12 @@ populate_lr_context(struct
> >i915_gem_context
> >> >*ctx,
> >> >>                 return ret;
> >> >>         }
> >> >>
> >> >> -       vaddr = i915_gem_object_pin_map(ctx_obj, I915_MAP_WB);
> >> >> +       vaddr = i915_gem_object_pin_map(ctx_obj, map);
> >> >
> >> >As this uses the cpu domain and flushed afterwards, this one is
> >> >correct in its usage of MAP_WB.
> >>
> >> In this function the content of context state is flushed.
> >>
> >> But the function of execlists_submit_ports will update it again before writing
> >the ELSP port.
> >> And there is no flush. In fact after the ELSP port is written, the HW will start
> >to execute the submitted commands.
> >
> >That's a different map.
> 
> Really?  It is allocated in one gem obj.
> 
> Will you please help to point out where to handle the different map?

It is reallocated on demand. The map used to prepopulate the context
image is not the same map used to update the ring registers in flight.
-Chris