[NPKit] Use default output directory when env var is not set (#1747)

src/init.cc

@@ -2558,10 +2558,17 @@ static ncclResult_t commCleanup(ncclComm_t comm) {
   // Dump NPKit events and shutdown
   const char* npkitDumpDir = getenv("NPKIT_DUMP_DIR");
   if (npkitDumpDir == nullptr) {
-    WARN("NPKIT_DUMP_DIR is empty");
-  } else {
-    NCCLCHECK(NpKit::Dump(npkitDumpDir));
+    npkitDumpDir = "./npkit_dump";
+    INFO(NCCL_INIT, "NPKIT_DUMP_DIR is not set, using default directory: %s", npkitDumpDir);
+
+    struct stat st;
+    if (stat(npkitDumpDir, &st) != 0) {
+      if (mkdir(npkitDumpDir, 0755) != 0) {
+        WARN("Failed to create NPKIT_DUMP_DIR directory: %s", npkitDumpDir);
+      }
+    }
   }
+  NCCLCHECK(NpKit::Dump(npkitDumpDir));
   NCCLCHECK(NpKit::Shutdown());
 #endif