drm/i915: Convert non-blocking userptr waits for requests over to using RCU

We can completely avoid taking the struct_mutex around the non-blocking
waits by switching over to the RCU request management (trading the mutex
for a RCU read lock and some complex atomic operations). The improvement
is that we gain further contention reduction, and overall the code
become simpler due to the reduced mutex dancing.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470388464-28458-3-git-send-email-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 53f64fcc89ef831fd794719f433376290e9c7d93..96ab6161903a28679be4124813825035a3918592 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -63,32 +63,12 @@ struct i915_mmu_object {
 
 static void wait_rendering(struct drm_i915_gem_object *obj)
 {
-       struct drm_device *dev = obj->base.dev;
-       struct drm_i915_gem_request *requests[I915_NUM_ENGINES];
-       int i, n;
-
-       if (!i915_gem_object_is_active(obj))
-               return;
-
-       n = 0;
-       for (i = 0; i < I915_NUM_ENGINES; i++) {
-               struct drm_i915_gem_request *req;
+       unsigned long active = __I915_BO_ACTIVE(obj);
+       int idx;
 
-               req = i915_gem_active_get(&obj->last_read[i],
-                                         &obj->base.dev->struct_mutex);
-               if (req)
-                       requests[n++] = req;
-       }
-
-       mutex_unlock(&dev->struct_mutex);
-
-       for (i = 0; i < n; i++)
-               i915_wait_request(requests[i], false, NULL, NULL);
-
-       mutex_lock(&dev->struct_mutex);
-
-       for (i = 0; i < n; i++)
-               i915_gem_request_put(requests[i]);
+       for_each_active(active, idx)
+               i915_gem_active_wait_unlocked(&obj->last_read[idx],
+                                             false, NULL, NULL);
 }
 
 static void cancel_userptr(struct work_struct *work)
@@ -97,6 +77,8 @@ static void cancel_userptr(struct work_struct *work)
        struct drm_i915_gem_object *obj = mo->obj;
        struct drm_device *dev = obj->base.dev;
 
+       wait_rendering(obj);
+
        mutex_lock(&dev->struct_mutex);
        /* Cancel any active worker and force us to re-evaluate gup */
        obj->userptr.work = NULL;
@@ -105,8 +87,6 @@ static void cancel_userptr(struct work_struct *work)
                struct drm_i915_private *dev_priv = to_i915(dev);
                bool was_interruptible;
 
-               wait_rendering(obj);
-
                was_interruptible = dev_priv->mm.interruptible;
                dev_priv->mm.interruptible = false;