Re: [PATCH 17/28] drm/i915: use the new iterator in i915_gem_busy_ioctl v2

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On 01/10/2021 11:05, Christian König wrote:
This makes the function much simpler since the complex
retry logic is now handled else where.

Signed-off-by: Christian König <christian.koenig@xxxxxxx>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Sorry I retract until you add the text about the increased cost of the added atomics. I think the point is important to discuss given proposal goes from zero atomics to num_fences * 2 (fence get/put unless I am mistaken) atomics per busy ioctl. That makes me lean towards just leaving this as is since it is not that complex.

Regards,

Tvrtko

---
  drivers/gpu/drm/i915/gem/i915_gem_busy.c | 35 ++++++++++--------------
  1 file changed, 14 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_busy.c b/drivers/gpu/drm/i915/gem/i915_gem_busy.c
index 6234e17259c1..dc72b36dae54 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_busy.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_busy.c
@@ -82,8 +82,8 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
  {
  	struct drm_i915_gem_busy *args = data;
  	struct drm_i915_gem_object *obj;
-	struct dma_resv_list *list;
-	unsigned int seq;
+	struct dma_resv_iter cursor;
+	struct dma_fence *fence;
  	int err;
err = -ENOENT;
@@ -109,27 +109,20 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
  	 * to report the overall busyness. This is what the wait-ioctl does.
  	 *
  	 */
-retry:
-	seq = raw_read_seqcount(&obj->base.resv->seq);
-
-	/* Translate the exclusive fence to the READ *and* WRITE engine */
-	args->busy = busy_check_writer(dma_resv_excl_fence(obj->base.resv));
-
-	/* Translate shared fences to READ set of engines */
-	list = dma_resv_shared_list(obj->base.resv);
-	if (list) {
-		unsigned int shared_count = list->shared_count, i;
-
-		for (i = 0; i < shared_count; ++i) {
-			struct dma_fence *fence =
-				rcu_dereference(list->shared[i]);
-
+	args->busy = 0;
+	dma_resv_iter_begin(&cursor, obj->base.resv, true);
+	dma_resv_for_each_fence_unlocked(&cursor, fence) {
+		if (dma_resv_iter_is_restarted(&cursor))
+			args->busy = 0;
+
+		if (dma_resv_iter_is_exclusive(&cursor))
+			/* Translate the exclusive fence to the READ *and* WRITE engine */
+			args->busy |= busy_check_writer(fence);
+		else
+			/* Translate shared fences to READ set of engines */
  			args->busy |= busy_check_reader(fence);
-		}
  	}
-
-	if (args->busy && read_seqcount_retry(&obj->base.resv->seq, seq))
-		goto retry;
+	dma_resv_iter_end(&cursor);
err = 0;
  out:




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