[Intel-gfx] [PATCH] drm/i915: Track dirtying of CPU cache for LLC

[Chris Wilson]

Doing mixed rendering into the front/back scanout buffers lead to the
interesting rediscovery of clflushing when page-flipping. A painful
experience indeed.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h |    1 +
 drivers/gpu/drm/i915/i915_gem.c |    7 +++++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 4eee0bf..569475b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -865,6 +865,7 @@ struct drm_i915_gem_object {
 	unsigned int fenced_gpu_access:1;
 
 	unsigned int cache_level:2;
+	unsigned int cache_dirty:2;
 
 	unsigned int has_aliasing_ppgtt_mapping:1;
 
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index eb63c69..8e547dd 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2907,12 +2907,15 @@ i915_gem_clflush_object(struct drm_i915_gem_object *obj)
 	 * snooping behaviour occurs naturally as the result of our domain
 	 * tracking.
 	 */
-	if (obj->cache_level != I915_CACHE_NONE)
+	if (obj->cache_level != I915_CACHE_NONE) {
+		obj->cache_dirty = obj->cache_level;
 		return;
+	}
 
 	trace_i915_gem_object_clflush(obj);
 
 	drm_clflush_pages(obj->pages, obj->base.size / PAGE_SIZE);
+	obj->cache_dirty = I915_CACHE_NONE;
 }
 
 /** Flushes any GPU write domain for the object if it's dirty. */
@@ -3066,7 +3069,7 @@ int i915_gem_object_set_cache_level(struct drm_i915_gem_object *obj,
 					       obj, cache_level);
 	}
 
-	if (cache_level == I915_CACHE_NONE) {
+	if (obj->cache_dirty) {
 		u32 old_read_domains, old_write_domain;
 
 		/* If we're coming from LLC cached, then we haven't
-- 
1.7.9.1