[PATCH 13/13] drm/i915: Use the LLC mode on gen6 for everything but display.

Chris Wilson
2011-04-14T09:04:02Z

From: Eric Anholt <eric@anholt.net>

Improves full-screen openarena on my laptop 20.3% +/- 4.0% (n=3)
Improves 800x600 nexuiz on my laptop 12.3% +/- 0.1% (n=3)

We have more room to improve with doing LLC caching for display using
GFDT, and in doing LLC+MLC caching, but this was an easy performance
win and incremental improvement toward those two.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
drivers/gpu/drm/i915/i915_gem.c | 18 +++++++++++++++++-
1 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 46b63c3..7992308 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3704,7 +3704,23 @@ struct drm_i915_gem_object *i915_gem_alloc_object(struct drm_device *dev,
obj->base.write_domain = I915_GEM_DOMAIN_CPU;
obj->base.read_domains = I915_GEM_DOMAIN_CPU;

- obj->cache_level = I915_CACHE_NONE;
+ if (IS_GEN6(dev)) {
+ /* On Gen6, we can have the GPU use the LLC (the CPU
+ * cache) for about a 10% performance improvement
+ * compared to uncached. Graphics requests other than
+ * display scanout are coherent with the CPU in
+ * accessing this cache. This means in this mode we
+ * don't need to clflush on the CPU side, and on the
+ * GPU side we only need to flush internal caches to
+ * get data visible to the CPU.
+ *
+ * However, we maintain the display planes as UC, and so
+ * need to rebind when first used as such.
+ */
+ obj->cache_level = I915_CACHE_LLC;
+ } else
+ obj->cache_level = I915_CACHE_NONE;
+
obj->base.driver_private = NULL;
obj->fence_reg = I915_FENCE_REG_NONE;
INIT_LIST_HEAD(&obj->mm_list);
--
1.7.4.1