[Intel-gfx] [PATCH 1/3] drm/i915: Map the ringbuffer using WB on LLC machines

[Ville Syrjälä]

On Thu, Oct 08, 2015 at 01:39:54PM +0100, Chris Wilson wrote:
> If we have llc coherency, we can write directly into the ringbuffer
> using ordinary cached writes rather than forcing WC access.
> 
> v2: An important consequence is that we can forgo the mappable request
> for WB ringbuffers, allowing for many more simultaneous contexts.

Fits in with my understanding on llc coherency.

Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c | 70 ++++++++++++++++++++++++++-------
>  1 file changed, 56 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index d608be46ea6e..f81ec7785fac 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -1966,11 +1966,35 @@ static int init_phys_status_page(struct intel_engine_cs *ring)
>  
>  void intel_unpin_ringbuffer_obj(struct intel_ringbuffer *ringbuf)
>  {
> -	iounmap(ringbuf->virtual_start);
> +	if (HAS_LLC(ringbuf->obj->base.dev) && !ringbuf->obj->stolen)
> +		vunmap(ringbuf->virtual_start);
> +	else
> +		iounmap(ringbuf->virtual_start);
>  	ringbuf->virtual_start = NULL;
>  	i915_gem_object_ggtt_unpin(ringbuf->obj);
>  }
>  
> +static u32 *vmap_obj(struct drm_i915_gem_object *obj)
> +{
> +	struct sg_page_iter sg_iter;
> +	struct page **pages;
> +	void *addr;
> +	int i;
> +
> +	pages = drm_malloc_ab(obj->base.size >> PAGE_SHIFT, sizeof(*pages));
> +	if (pages == NULL)
> +		return NULL;
> +
> +	i = 0;
> +	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, 0)
> +		pages[i++] = sg_page_iter_page(&sg_iter);
> +
> +	addr = vmap(pages, i, 0, PAGE_KERNEL);
> +	drm_free_large(pages);
> +
> +	return addr;
> +}
> +
>  int intel_pin_and_map_ringbuffer_obj(struct drm_device *dev,
>  				     struct intel_ringbuffer *ringbuf)
>  {
> @@ -1978,21 +2002,39 @@ int intel_pin_and_map_ringbuffer_obj(struct drm_device *dev,
>  	struct drm_i915_gem_object *obj = ringbuf->obj;
>  	int ret;
>  
> -	ret = i915_gem_obj_ggtt_pin(obj, PAGE_SIZE, PIN_MAPPABLE);
> -	if (ret)
> -		return ret;
> +	if (HAS_LLC(dev_priv) && !obj->stolen) {
> +		ret = i915_gem_obj_ggtt_pin(obj, PAGE_SIZE, 0);
> +		if (ret)
> +			return ret;
>  
> -	ret = i915_gem_object_set_to_gtt_domain(obj, true);
> -	if (ret) {
> -		i915_gem_object_ggtt_unpin(obj);
> -		return ret;
> -	}
> +		ret = i915_gem_object_set_to_cpu_domain(obj, true);
> +		if (ret) {
> +			i915_gem_object_ggtt_unpin(obj);
> +			return ret;
> +		}
> +
> +		ringbuf->virtual_start = vmap_obj(obj);
> +		if (ringbuf->virtual_start == NULL) {
> +			i915_gem_object_ggtt_unpin(obj);
> +			return -ENOMEM;
> +		}
> +	} else {
> +		ret = i915_gem_obj_ggtt_pin(obj, PAGE_SIZE, PIN_MAPPABLE);
> +		if (ret)
> +			return ret;
>  
> -	ringbuf->virtual_start = ioremap_wc(dev_priv->gtt.mappable_base +
> -			i915_gem_obj_ggtt_offset(obj), ringbuf->size);
> -	if (ringbuf->virtual_start == NULL) {
> -		i915_gem_object_ggtt_unpin(obj);
> -		return -EINVAL;
> +		ret = i915_gem_object_set_to_gtt_domain(obj, true);
> +		if (ret) {
> +			i915_gem_object_ggtt_unpin(obj);
> +			return ret;
> +		}
> +
> +		ringbuf->virtual_start = ioremap_wc(dev_priv->gtt.mappable_base +
> +						    i915_gem_obj_ggtt_offset(obj), ringbuf->size);
> +		if (ringbuf->virtual_start == NULL) {
> +			i915_gem_object_ggtt_unpin(obj);
> +			return -EINVAL;
> +		}
>  	}
>  
>  	return 0;
> -- 
> 2.6.1
> 
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-- 
Ville Syrjälä
Intel OTC