To allow faster engine to engine synchronization, peel the layer of
dma-fence-chain to expose potential i915 fences so that the
i915-request code can emit HW semaphore wait/signal operations in the
ring which is faster than waking up the host to submit unblocked
workloads after interrupt notification.
v2: Also deal with chains where the last node is not a dma-fence-chain
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
.../gpu/drm/i915/gem/i915_gem_execbuffer.c | 39 ++++++++++++++++++-
1 file changed, 38 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 652f3b30a374..01e22b303e34 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -2390,6 +2390,7 @@ await_fence_array(struct i915_execbuffer *eb)
for (n = 0; n < eb->n_fences; n++) {
struct drm_syncobj *syncobj;
+ struct dma_fence_chain *chain;
struct dma_fence *fence;
unsigned int flags;
@@ -2410,7 +2411,43 @@ await_fence_array(struct i915_execbuffer *eb)
continue;
}
- err = i915_request_await_dma_fence(eb->request, fence);
+ chain = to_dma_fence_chain(fence);
+ if (chain) {
+ struct dma_fence *iter;
+
+ /*
+ * If we're dealing with a dma-fence-chain, peel the
+ * chain by adding all of the unsignaled fences
+ * (dma_fence_chain_for_each does that for us) the
+ * chain points to.
+ *
+ * This enables us to identify waits on i915 fences
+ * and allows for faster engine-to-engine
+ * synchronization using HW semaphores.
+ */
+ dma_fence_chain_for_each(iter, fence) {
+ struct dma_fence_chain *iter_chain =
+ to_dma_fence_chain(iter);
+
+ /*
+ * It is possible that the last item in the
+ * chain is not a dma_fence_chain.
+ */
+ if (iter_chain) {
+ err = i915_request_await_dma_fence(eb->request,
+ iter_chain->fence);
+ } else {
+ err = i915_request_await_dma_fence(eb->request, iter);
+ }
+ if (err < 0) {
+ dma_fence_put(iter);
+ break;
+ }
+ }
+ } else {
+ err = i915_request_await_dma_fence(eb->request, fence);
+ }
+
dma_fence_put(fence);
if (err < 0)
return err;
--
2.28.0
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