On 10/04/2020 19:51, Venkata Sandeep Dhanalakota wrote:
From: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
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.
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
---
.../gpu/drm/i915/gem/i915_gem_execbuffer.c | 39 +++++++++++++++++--
1 file changed, 35 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 8dd651cdca39..e43b76d7e9fd 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -2508,6 +2508,7 @@ await_fence_array(struct i915_execbuffer *eb,
for (n = 0; n < nfences; n++) {
struct drm_syncobj *syncobj;
+ struct dma_fence_chain *chain;
unsigned int flags;
syncobj = ptr_unpack_bits(fences[n].syncobj, &flags, 2);
@@ -2515,10 +2516,40 @@ await_fence_array(struct i915_execbuffer *eb,
if (!fences[n].dma_fence)
continue;
- err = i915_request_await_dma_fence(eb->request,
- fences[n].dma_fence);
- if (err < 0)
- return err;
+ /*
+ * 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.
+ */
+ chain = to_dma_fence_chain(fences[n].dma_fence);
+ if (chain) {
+ struct dma_fence *iter;
+
+ dma_fence_chain_for_each(iter, fences[n].dma_fence) {
The kbuild bot made me think of an interesting case.
It is possible to build a chain where the first element isn't a
dma_fence_chain.
We should handle this here like this :
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);
return err;
}
+ struct dma_fence_chain *iter_chain =
+ to_dma_fence_chain(iter);
+
+ GEM_BUG_ON(!iter_chain);
+
+ err = i915_request_await_dma_fence(eb->request,
+ iter_chain->fence);
+ if (err < 0) {
+ dma_fence_put(iter);
+ return err;
+ }
+ }
+
+ } else {
+ err = i915_request_await_dma_fence(eb->request,
+ fences[n].dma_fence);
+ if (err < 0)
+ return err;
+ }
}
return 0;
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