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

Ville Syrjälä
2015-10-16T14:55:45Z

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@linux.intel.com>

>
> Signed-off-by: Chris Wilson <chris@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