Cleanup number of channels calculation (#340)

[ROCm/rccl commit: e26ad2995e]

projects/rccl/src/graph/connect.cc

@@ -240,7 +240,7 @@ int ncclMaxNchannels() {
   return maxNchannels;
 }
 
-ncclResult_t ncclTopoPostset(struct ncclComm* comm, int* firstRanks, int* treePatterns, struct ncclTopoRanks** allTopoRanks, int* rings, int gcn, int nnets) {
+ncclResult_t ncclTopoPostset(struct ncclComm* comm, int* firstRanks, int* treePatterns, struct ncclTopoRanks** allTopoRanks, int* rings, int nc) {
   // Gather data from all ranks
   int *ringRecv, *ringSend, *ringPrev, *ringNext, *treeToParent, *treeToChild0, *treeToChild1;
   int nranks = comm->nRanks;
@@ -272,13 +272,6 @@ ncclResult_t ncclTopoPostset(struct ncclComm* comm, int* firstRanks, int* treePa
   memcpy(ringPrev+nChannels*nranks, ringPrev, nChannels*nranks*sizeof(int));
   memcpy(ringNext+nChannels*nranks, ringNext, nChannels*nranks*sizeof(int));
 
-  int nc = nChannels*2;
-  if (gcn == 908) nc = std::max(nc, 4);
-  if (comm->topo->nodes[GPU].count == comm->topo->nRanks && (comm->topo->type & RCCL_TOPO_CR8G)) nc = nChannels*4;
-  if (!nnets) nnets = comm->topo->nodes[NET].count;
-  if (nnets && (comm->topo->type & RCCL_TOPO_4P2H_ROME)) nc = (nnets > 3 ? 2 : 4)*nnets;
-  int end = std::min((int)ncclMaxNchannels(), std::max(nc, ncclMinNchannels()));
-
   // Duplication should be complete now
   nChannels = comm->nChannels = std::min(MAXCHANNELS,nChannels*2);
 
@@ -286,7 +279,7 @@ ncclResult_t ncclTopoPostset(struct ncclComm* comm, int* firstRanks, int* treePa
   // We permit combining max, then min, to only use the first channels, then duplicate them.
   nChannels = comm->nChannels = std::min((int)ncclMaxNchannels(), nChannels);
   int c;
-  for (c=nChannels; c<end; c++) {
+  for (c=nChannels; c<std::min((int)ncclMaxNchannels(), std::max(nc, ncclMinNchannels())); c++) {
     memcpy(ringPrev+c*nranks, ringPrev+(c-nChannels)*nranks, nranks*sizeof(int));
     memcpy(ringNext+c*nranks, ringNext+(c-nChannels)*nranks, nranks*sizeof(int));
     memcpy(comm->channels+c, comm->channels+c-nChannels, sizeof(struct ncclChannel));