[BUILD] Populate host_table entries only for 1 unroll (#1871)

src/device/generate.py

@@ -267,6 +267,7 @@ def equivalent_primary(coll, algo, proto, redop, ty, acc, unroll):
   return (coll, algo, proto, redop, ty, acc, unroll)
 
 # Order rows are enumerated must match formula of `ncclDevFuncId()`:
+# outermost loop should be for unroll factor; refer to host_table section
 def enumerate_func_rows():
   for unroll in all_unroll:
     for acc in use_acc:
@@ -474,7 +475,11 @@ with open(os.path.join(gensrc, "host_table.cpp"), "w") as f:
   out("//   bits 16-19:  ty index\n")
   out("#include <unordered_map>\n")
   out("extern std::unordered_map<uint64_t, int> ncclDevFuncNameToId = {\n")
-  for fn in func_rows:
+
+  # host_table entries map device functions based on collective, algorithm, protocol, redop, and datatype
+  # For GPU targets that support multiple unrolls, e.g., gfx950
+  # (or) for non-local builds, only a single set of functions are needed in the host_table.
+  for fn in func_rows[:len(func_rows)//len(all_unroll)]:
     fn_id = -1
     if fn is not None:
       fn_id = primary_to_index[equivalent_primary(*fn)]