[Intel-gfx] [PATCH 19/33] drm/i915: Only clflush the context object when binding

[Chris Wilson]

On Wed, Aug 10, 2016 at 11:41:39AM +0300, Joonas Lahtinen wrote:
> On su, 2016-08-07 at 15:45 +0100, Chris Wilson wrote:
> > @@ -771,6 +771,13 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
> >  	if (skip_rcs_switch(ppgtt, engine, to))
> >  		return 0;
> >  
> > +	if (!(to->engine[RCS].state->flags & I915_VMA_GLOBAL_BIND)) {
> > +		ret = i915_gem_object_set_to_gtt_domain(to->engine[RCS].state->obj,
> > +							false);
> > +		if (ret)
> > +			return ret;
> > +	}
> > +
> >  	/* Trying to pin first makes error handling easier. */
> >  	ret = i915_vma_pin(to->engine[RCS].state,
> >  			   0, to->ggtt_alignment,
> 
> This could be lifted inside the if?

I'd rather not as that would be more unusual and we would then need a
complicated error path.

If the compiler is feeling intelligent it could combine the two blocks
into one, i.e.

if (unlikely((++vma->flags ^ flags) & I915_VMA_BIND_MASK)) {
	ret = i915_gem_object_set_to_gtt_domain(vma->obj, false);
	if (ret)
		return ret;

	ret = __i915_vma_do_pin(vma, size, alignment, flags);
	if (ret)
		return ret;
}

I don't suggest we do the expansion ourselves, and I don't have a bit to
spare in the PIN_FLAGS.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre