From d6d6af710e10d0457e51b0ef0225e291cb924052 Mon Sep 17 00:00:00 2001
From: Wenkai Du <43822138+wenkaidu@users.noreply.github.com>
Date: Fri, 4 Mar 2022 10:29:02 -0800
Subject: [PATCH] Force ring algorithm on single node (#509)

---
 src/graph/tuning.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/graph/tuning.cc b/src/graph/tuning.cc
index f8c4a17f18..df51c6e71b 100644
--- a/src/graph/tuning.cc
+++ b/src/graph/tuning.cc
@@ -126,7 +126,7 @@ ncclResult_t ncclTopoTuneModel(struct ncclComm* comm, int minCompCap, int maxCom
       nNodes;
 
     for (int a=0; a<NCCL_NUM_ALGORITHMS; a++) {
-      if (coll != ncclFuncAllReduce && a != NCCL_ALGO_RING) continue;
+      if ((coll != ncclFuncAllReduce || nNodes == 1) && a != NCCL_ALGO_RING) continue;
 
       for (int p=0; p<NCCL_NUM_PROTOCOLS; p++) {
         float speed = nNodes <= 2 || a == NCCL_ALGO_COLLNET ? graphs[a]->speedIntra : graphs[a]->speedInter;