drm/i915: Only wait on a pending flip if we intend to write to the buffer

... as if we are only reading from it, we can do that concurrently with
the queue flip.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 44 insertions, 48 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index d461ad5f9290..8513c04dc892 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -37,6 +37,7 @@ struct change_domains {
         uint32_t invalidate_domains;
         uint32_t flush_domains;
         uint32_t flush_rings;
+        uint32_t flips;
 };
 
 /*
@@ -190,6 +191,9 @@ i915_gem_object_set_to_gpu_domain(struct drm_i915_gem_object *obj,
         if ((flush_domains | invalidate_domains) & I915_GEM_DOMAIN_GTT)
                 i915_gem_release_mmap(obj);
 
+        if (obj->base.pending_write_domain)
+                cd->flips |= atomic_read(&obj->pending_flip);
+
         /* The actual obj->write_domain will be updated with
          * pending_write_domain after we emit the accumulated flush for all
          * of our domain changes in execbuffers (which clears objects'
@@ -774,6 +778,39 @@ i915_gem_execbuffer_sync_rings(struct drm_i915_gem_object *obj,
 }
 
 static int
+i915_gem_execbuffer_wait_for_flips(struct intel_ring_buffer *ring, u32 flips)
+{
+        u32 plane, flip_mask;
+        int ret;
+
+        /* Check for any pending flips. As we only maintain a flip queue depth
+         * of 1, we can simply insert a WAIT for the next display flip prior
+         * to executing the batch and avoid stalling the CPU.
+         */
+
+        for (plane = 0; flips >> plane; plane++) {
+                if (((flips >> plane) & 1) == 0)
+                        continue;
+
+                if (plane)
+                        flip_mask = MI_WAIT_FOR_PLANE_B_FLIP;
+                else
+                        flip_mask = MI_WAIT_FOR_PLANE_A_FLIP;
+
+                ret = intel_ring_begin(ring, 2);
+                if (ret)
+                        return ret;
+
+                intel_ring_emit(ring, MI_WAIT_FOR_EVENT | flip_mask);
+                intel_ring_emit(ring, MI_NOOP);
+                intel_ring_advance(ring);
+        }
+
+        return 0;
+}
+
+
+static int
 i915_gem_execbuffer_move_to_gpu(struct intel_ring_buffer *ring,
                                 struct list_head *objects)
 {
@@ -781,9 +818,7 @@ i915_gem_execbuffer_move_to_gpu(struct intel_ring_buffer *ring,
         struct change_domains cd;
         int ret;
 
-        cd.invalidate_domains = 0;
-        cd.flush_domains = 0;
-        cd.flush_rings = 0;
+        memset(&cd, 0, sizeof(cd));
         list_for_each_entry(obj, objects, exec_list)
                 i915_gem_object_set_to_gpu_domain(obj, ring, &cd);
 
@@ -796,6 +831,12 @@ i915_gem_execbuffer_move_to_gpu(struct intel_ring_buffer *ring,
                         return ret;
         }
 
+        if (cd.flips) {
+                ret = i915_gem_execbuffer_wait_for_flips(ring, cd.flips);
+                if (ret)
+                        return ret;
+        }
+
         list_for_each_entry(obj, objects, exec_list) {
                 ret = i915_gem_execbuffer_sync_rings(obj, ring);
                 if (ret)
@@ -842,47 +883,6 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
         return 0;
 }
 
-static int
-i915_gem_execbuffer_wait_for_flips(struct intel_ring_buffer *ring,
-                                   struct list_head *objects)
-{
-        struct drm_i915_gem_object *obj;
-        int flips;
-
-        /* Check for any pending flips. As we only maintain a flip queue depth
-         * of 1, we can simply insert a WAIT for the next display flip prior
-         * to executing the batch and avoid stalling the CPU.
-         */
-        flips = 0;
-        list_for_each_entry(obj, objects, exec_list) {
-                if (obj->base.write_domain)
-                        flips |= atomic_read(&obj->pending_flip);
-        }
-        if (flips) {
-                int plane, flip_mask, ret;
-
-                for (plane = 0; flips >> plane; plane++) {
-                        if (((flips >> plane) & 1) == 0)
-                                continue;
-
-                        if (plane)
-                                flip_mask = MI_WAIT_FOR_PLANE_B_FLIP;
-                        else
-                                flip_mask = MI_WAIT_FOR_PLANE_A_FLIP;
-
-                        ret = intel_ring_begin(ring, 2);
-                        if (ret)
-                                return ret;
-
-                        intel_ring_emit(ring, MI_WAIT_FOR_EVENT | flip_mask);
-                        intel_ring_emit(ring, MI_NOOP);
-                        intel_ring_advance(ring);
-                }
-        }
-
-        return 0;
-}
-
 static void
 i915_gem_execbuffer_move_to_active(struct list_head *objects,
                                    struct intel_ring_buffer *ring,
@@ -1133,10 +1133,6 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
         if (ret)
                 goto err;
 
-        ret = i915_gem_execbuffer_wait_for_flips(ring, &objects);
-        if (ret)
-                goto err;
-
         seqno = i915_gem_next_request_seqno(ring);
         for (i = 0; i < ARRAY_SIZE(ring->sync_seqno); i++) {
                 if (seqno < ring->sync_seqno[i]) {