[BE] Improve input mismatch error msg

Test Plan: CI Differential Revision: D48363238 fbshipit-source-id: 4740853d31b4c87915766a79749902d46409ac53
pytorch · Aug 16, 2023 · a17af5f · a17af5f
1 parent 35cca79
commit a17af5f
Showing 1 changed file with 10 additions and 2 deletions.
diff --git a/torch/csrc/distributed/c10d/ProcessGroupNCCL.cpp b/torch/csrc/distributed/c10d/ProcessGroupNCCL.cpp
@@ -1502,8 +1502,16 @@ std::vector<at::Tensor> flatten_for_scatter_gather(
     if (tensor_lists[i].size() != world_size * num_devices) {
       TORCH_CHECK(
           false,
-          "Tensor list input to scatter/gather must match number of collective"
-          " participants");
+          c10::str(
+              "Tensor list input to scatter/gather must match number of collective participants ",
+              "but got ",
+              tensor_lists[i].size(),
+              " inputs",
+              " with world_size",
+              world_size,
+              " and ",
+              num_devices,
+              " devices."));
     }
 
     // Only check device match for the first tensor in the list; the call to