drm/i915: Mark CPU cache as dirty on every transition for CPU writes

Currently, we only mark the CPU cache as dirty if we skip a clflush.
This leads to some confusion where we have to ask if the object is in
the write domain or missed a clflush. If we always mark the cache as
dirty, this becomes a much simply question to answer.

The goal remains to do as few clflushes as required and to do them as
late as possible, in the hope of deferring the work to a kthread and not
block the caller (e.g. execbuf, flips).

v2: Always call clflush before GPU execution when the cache_dirty flag
is set. This may cause some extra work on llc systems that migrate dirty
buffers back and forth - but we do try to limit that by only setting
cache_dirty at the end of the gpu sequence.

v3: Always mark the cache as dirty upon a level change, as we need to
invalidate any stale cachelines due to external writes.

Reported-by: Dongwon Kim <dongwon.kim@intel.com>
Fixes: a6a7cc4b7db6 ("drm/i915: Always flush the dirty CPU cache when pinning the scanout")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Dongwon Kim <dongwon.kim@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Tested-by: Dongwon Kim <dongwon.kim@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170615123850.26843-1-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

1 files changed, 7 insertions, 8 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_clflush.c b/drivers/gpu/drm/i915/i915_gem_clflush.c
index ffac7a1f0caf..17b207e963c2 100644
--- a/drivers/gpu/drm/i915/i915_gem_clflush.c
+++ b/drivers/gpu/drm/i915/i915_gem_clflush.c
@@ -71,8 +71,6 @@ static const struct dma_fence_ops i915_clflush_ops = {
 static void __i915_do_clflush(struct drm_i915_gem_object *obj)
 {
 	drm_clflush_sg(obj->mm.pages);
-	obj->cache_dirty = false;
-
 	intel_fb_obj_flush(obj, ORIGIN_CPU);
 }
 
@@ -81,9 +79,6 @@ static void i915_clflush_work(struct work_struct *work)
 	struct clflush *clflush = container_of(work, typeof(*clflush), work);
 	struct drm_i915_gem_object *obj = clflush->obj;
 
-	if (!obj->cache_dirty)
-		goto out;
-
 	if (i915_gem_object_pin_pages(obj)) {
 		DRM_ERROR("Failed to acquire obj->pages for clflushing\n");
 		goto out;
@@ -131,10 +126,10 @@ void i915_gem_clflush_object(struct drm_i915_gem_object *obj,
 	 * anything not backed by physical memory we consider to be always
 	 * coherent and not need clflushing.
 	 */
-	if (!i915_gem_object_has_struct_page(obj))
+	if (!i915_gem_object_has_struct_page(obj)) {
+		obj->cache_dirty = false;
 		return;
-
-	obj->cache_dirty = true;
+	}
 
 	/* If the GPU is snooping the contents of the CPU cache,
 	 * we do not need to manually clear the CPU cache lines.  However,
@@ -153,6 +148,8 @@ void i915_gem_clflush_object(struct drm_i915_gem_object *obj,
 	if (!(flags & I915_CLFLUSH_SYNC))
 		clflush = kmalloc(sizeof(*clflush), GFP_KERNEL);
 	if (clflush) {
+		GEM_BUG_ON(!obj->cache_dirty);
+
 		dma_fence_init(&clflush->dma,
 			       &i915_clflush_ops,
 			       &clflush_lock,
@@ -180,4 +177,6 @@ void i915_gem_clflush_object(struct drm_i915_gem_object *obj,
 	} else {
 		GEM_BUG_ON(obj->base.write_domain != I915_GEM_DOMAIN_CPU);
 	}
+
+	obj->cache_dirty = false;
 }