Fix ring_exchange RS to support CUDA graph capture (#811)

Signed-off-by: Vasudevan Rengasamy <vrengasamy@nvidia.com>
Co-authored-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

transformer_engine/pytorch/csrc/comm_gemm_overlap.h

@@ -99,7 +99,7 @@ struct UbufCommOverlap : torch::CustomClassHolder, UbufBase {
     }
     _ubuf = torch::from_blob(_ubuf_ptr, {sample.size(0), sample.size(1)}, sample.options());
 
-    at::cuda::CUDAStream stream_main = at::cuda::getDefaultCUDAStream();
+    at::cuda::CUDAStream stream_main = at::cuda::getCurrentCUDAStream();
     for (int i = 0; i < std::min(num_max_streams, num_splits); i++) {
       cudaStream_t stream;
       cudaStreamCreateWithPriority(&stream, cudaStreamNonBlocking, -1);
@@ -596,7 +596,7 @@ struct UbufP2PCommOverlap : torch::CustomClassHolder, UbufBase {
       ubuf_byte_ptr += ubuf_chunk_bytes;
     }
 
-    at::cuda::CUDAStream stream_main = at::cuda::getDefaultCUDAStream();
+    at::cuda::CUDAStream stream_main = at::cuda::getCurrentCUDAStream();
     for (int i = 0; i < std::min(num_max_streams, tp_size); i++) {
       cudaStream_t stream;
       cudaStreamCreateWithPriority(&stream, cudaStreamNonBlocking, -1);
@@ -691,7 +691,7 @@ struct UbufP2PCommOverlap : torch::CustomClassHolder, UbufBase {
     assert(pre_gelu_out.numel() == 0);
 
     // Catch up the default torch stream
-    at::cuda::CUDAStream stream_main = at::cuda::getDefaultCUDAStream();
+    at::cuda::CUDAStream stream_main = at::cuda::getCurrentCUDAStream();
     CHECK_CUDA(cudaEventRecord(_start_compute, (cudaStream_t)stream_main));
     CHECK_CUDA(cudaStreamWaitEvent((cudaStream_t)_stream_send, _start_compute, 0));
     CHECK_CUDA(cudaStreamWaitEvent((cudaStream_t)_stream_recv, _start_compute, 0));
@@ -974,7 +974,7 @@ struct UbufP2PCommOverlap : torch::CustomClassHolder, UbufBase {
       B_scale_inverse = B_scale_inverse[B_fp8_tensor];
 
     // Catch up the main stream
-    at::cuda::CUDAStream stream_main = at::cuda::getDefaultCUDAStream();
+    at::cuda::CUDAStream stream_main = at::cuda::getCurrentCUDAStream();
     CHECK_CUDA(cudaEventRecord(_start_compute, (cudaStream_t)stream_main));
     CHECK_CUDA(cudaStreamWaitEvent((cudaStream_t)_stream_recv, _start_compute, 0));
 
@@ -1055,8 +1055,10 @@ struct UbufP2PCommOverlap : torch::CustomClassHolder, UbufBase {
       B_scale_inverse = B_scale_inverse[B_fp8_tensor];
 
     // Catch up the main stream
-    at::cuda::CUDAStream stream_main = at::cuda::getDefaultCUDAStream();
+    at::cuda::CUDAStream stream_main = at::cuda::getCurrentCUDAStream();
     CHECK_CUDA(cudaEventRecord(_start_compute, (cudaStream_t)stream_main));
+    CHECK_CUDA(cudaStreamWaitEvent((cudaStream_t)_stream_send, _start_compute, 0));
+    CHECK_CUDA(cudaStreamWaitEvent((cudaStream_t)_stream_recv, _start_compute, 0));
     for (int i = 0; i < _stream_compute.size(); i++) {
         CHECK_CUDA(cudaStreamWaitEvent((cudaStream_t) _stream_compute[i], _start_compute, 0));
     }
@@ -1113,13 +1115,20 @@ struct UbufP2PCommOverlap : torch::CustomClassHolder, UbufBase {
         reduce_buf_ptr, {_tp_size, _ubufs[0].size(0), _ubufs[0].size(1)}, _ubuf.options());
       torch::sum_out(rs_output, reduce_buf, 0);
     }
+    for (int i = 0; i < _stream_compute.size(); i++) {
+      CHECK_CUDA(
+          cudaEventRecord(_stop_compute, (cudaStream_t)_stream_compute[i]));
+      CHECK_CUDA(cudaStreamWaitEvent((cudaStream_t)stream_main, _stop_compute, 0));
+    }
+    CHECK_CUDA(cudaEventRecord(_stop_send, (cudaStream_t)_stream_send));
+    CHECK_CUDA(cudaStreamWaitEvent((cudaStream_t)stream_main, _stop_send, 0));
   }
 
   /*
   ** Copy input to _ubufs[0]
   */
   void copy_input_to_ubuf(torch::Tensor input, bool chunk) {
-    at::cuda::CUDAStream stream_main = at::cuda::getDefaultCUDAStream();
+    at::cuda::CUDAStream stream_main = at::cuda::getCurrentCUDAStream();
     if (chunk) {
       // Copy input to the target ubuf chunk by rank offset
       if (input.numel() != _ubufs[0].numel() || input.element_size() != _ubufs[0].element_size()) {