diff --git a/doc/efa-env-var.md b/doc/efa-env-var.md
index cf75034e2..f5e04c56b 100644
--- a/doc/efa-env-var.md
+++ b/doc/efa-env-var.md
@@ -74,6 +74,11 @@ versions of your libfabric.
       behaves very differently, especially on newer kernels, where <code>RDMAV_FORK_SAFE=1</code>
       can break things.</td>
    </tr>
+   <tr>
+      <td><code>`NCCL_SHM_USE_CUDA_MEMCPY=1</code></td>
+      <td>Setting this when you run NCCL on g6/g5. It gives x2 performance in comparison to default memcpy.</td>
+   </tr>
+
    <tr>
       <td><code>RDMAV_*</code></td>
       <td>Do not use.</td>