[Intel-gfx] [PATCH 4/4] drm/i915: report all active objects as busy

[Daniel Vetter]

Reporting objects that are not currently used by the gpu but are
dirty and not yet flushed creates havoc to libdrm's bo reuse:
The usually immediatly following gtt_map afterwards will stall
until the gpu has executed the writeback.

Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/i915/i915_gem.c |   27 +++++++++++++++++++--------
 1 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 8e18c9d..7950169 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4395,14 +4395,25 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
 	i915_gem_retire_requests(dev);
 
 	obj_priv = to_intel_bo(obj);
-	/* Don't count being on the flushing list against the object being
-	 * done.  Otherwise, a buffer left on the flushing list but not getting
-	 * flushed (because nobody's flushing that domain) won't ever return
-	 * unbusy and get reused by libdrm's bo cache.  The other expected
-	 * consumer of this interface, OpenGL's occlusion queries, also specs
-	 * that the objects get unbusy "eventually" without any interference.
-	 */
-	args->busy = obj_priv->active && obj_priv->last_rendering_seqno != 0;
+
+	/* Count all active objects as busy, even if they are currently not used
+	 * by the gpu. Users of this interface expect objects to eventually
+	 * become non-busy without any further actions, therefore emit any
+	 * necessary flushes here. */
+	args->busy = obj_priv->active;
+
+	/* Unconditionally flush objects, even when the gpu still uses this
+	 * object. Userspace calling this function indicates that it wants to
+	 * use this buffer rather sooner than later, so issuing the required
+	 * flush earlier is beneficial. */
+	if (obj->write_domain) {
+		uint32_t seqno;
+
+		i915_gem_flush(dev, 0, obj->write_domain);
+		seqno = i915_add_request(dev, file_priv, obj->write_domain);
+		if (seqno == 0)
+			return -ENOMEM;
+	}
 
 	drm_gem_object_unreference(obj);
 	mutex_unlock(&dev->struct_mutex);
-- 
1.6.6.1