By applying the same logic as for wait-ioctl, we can query whether a
request has completed without holding struct_mutex. The biggest impact
system-wide is removing the flush_active and the contention that causes.

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c | 51 ++++++++++++++++++++++-------------------
 1 file changed, 28 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index f30207596ec6..95d4d2460f6a 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3559,34 +3559,39 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
 {
        struct drm_i915_gem_busy *args = data;
        struct drm_i915_gem_object *obj;
-       int ret;
-
-       ret = i915_mutex_lock_interruptible(dev);
-       if (ret)
-               return ret;
 
        obj = to_intel_bo(drm_gem_object_lookup(dev, file, args->handle));
-       if (&obj->base == NULL) {
-               ret = -ENOENT;
-               goto unlock;
-       }
+       if (&obj->base == NULL)
+               return -ENOENT;
 
-       /* 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.
-        */
-       i915_gem_object_flush_active(obj);
+       args->busy = 0;
+       if (__I915_BO_ACTIVE(obj)) {
+               struct drm_i915_gem_request *req;
+               int i;
 
-       BUILD_BUG_ON(I915_NUM_RINGS > 16);
-       args->busy = I915_BO_ACTIVE(obj) << 16;
-       if (obj->last_write.request)
-               args->busy |= obj->last_write.request->engine->id;
+               BUILD_BUG_ON(I915_NUM_RINGS > 16);
+               rcu_read_lock();
+               for (i = 0; i < I915_NUM_RINGS; i++) {
+                       req = 
i915_gem_active_get_request_rcu(&obj->last_read[i]);
+                       if (req == NULL)
+                               continue;
 
-       drm_gem_object_unreference(&obj->base);
-unlock:
-       mutex_unlock(&dev->struct_mutex);
-       return ret;
+                       if (!i915_gem_request_completed(req))
+                               args->busy |= 1 << (16 + i);
+                       i915_gem_request_put(req);
+               }
+
+               req = i915_gem_active_get_request_rcu(&obj->last_write);
+               if (req) {
+                       if (!i915_gem_request_completed(req))
+                               args->busy |= 1 << req->engine->id;
+                       i915_gem_request_put(req);
+               }
+               rcu_read_unlock();
+       }
+
+       drm_gem_object_unreference_unlocked(&obj->base);
+       return 0;
 }
 
 int
-- 
2.7.0.rc3

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