Add switch for pivot alltoall kernel (#549)

[ROCm/rccl commit: 6707a270b1]

projects/rccl/src/init.cc

@@ -356,6 +356,7 @@ static ncclResult_t commFree(ncclComm_t comm) {
 
 RCCL_PARAM(CliqueIgnoreTopo, "CLIQUE_IGNORE_TOPO", 0);
 RCCL_PARAM(P2pNetDisable, "P2P_NET_DISABLE", 0);
+RCCL_PARAM(PivotAlltoallEnable, "PIVOT_ALLTOALL_ENABLE", 0);
 NCCL_PARAM(AggChannelSize, "AGG_CHANNEL_SIZE", -2);
 NCCL_PARAM(DisableGraphHelper, "GRAPH_HELPER_DISABLE", 0);
 NCCL_PARAM(GraphRegister, "GRAPH_REGISTER", 0);
@@ -883,7 +884,7 @@ static ncclResult_t initTransportsRank(struct ncclComm* comm, ncclUniqueId* comm
   allGather3Data[rank].collNet.typeIntra = collNetGraph.typeIntra;
   allGather3Data[rank].collNet.typeInter = collNetGraph.typeInter;
   allGather3Data[rank].collNetSupport = comm->collNetSupport;
-  allGather3Data[rank].pivotA2AEnabled = comm->topo->pivotA2AEnabled;
+  allGather3Data[rank].pivotA2AEnabled = comm->topo->pivotA2AEnabled && rcclParamPivotAlltoallEnable();
 
   comm->nChannels = (comm->topo->nodes[GPU].count != comm->topo->nRanks && comm->topo->nodes[NET].count)
     ? std::min(treeGraph.nChannels, ringGraph.nChannels) : ringGraph.nChannels;