xuewanqi commented on a change in pull request #468: Distributted module
URL: https://github.com/apache/incubator-singa/pull/468#discussion_r300558656
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File path: src/dist/communicator.cc
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@@ -0,0 +1,150 @@
+#include "singa/dist/communicator.h"
+#include<iostream>
+namespace singa{
+
+static uint64_t getHostHash(const char* string) {
+ // Based on DJB2, result = result * 33 + char
+ uint64_t result = 5381;
+ for (int c = 0; string[c] != '\0'; c++){
+ result = ((result << 5) + result) + string[c];
+ }
+ return result;
+}
+
+
+static void getHostName(char* hostname, int maxlen) {
+ gethostname(hostname, maxlen);
+ for (int i=0; i< maxlen; i++) {
+ if (hostname[i] == '.') {
+ hostname[i] = '\0';
+ return;
+ }
+ }
+}
+
+
+Communicator::Communicator(int nDev): nDev(nDev){
+ MPICHECK(MPI_Init(NULL, NULL));
+ // get MPI Global Ranks and total Ranks
+ MPICHECK(MPI_Comm_rank(MPI_COMM_WORLD, &MPIRankInGlobal));
+ MPICHECK(MPI_Comm_size(MPI_COMM_WORLD, &totalMPIRanksInGlobal));
+ //std::cout<<"g rank " << MPIRankInGlobal << "\n";
+
+ //calculating MPIRankInLocal which is used in selecting a GPU
+ MPIRankInLocal=0;
+ uint64_t hostHashs[totalMPIRanksInGlobal];
+ char hostname[1024];
+ getHostName(hostname, 1024);
+ hostHashs[MPIRankInGlobal] = getHostHash(hostname);
+ MPICHECK(MPI_Allgather(MPI_IN_PLACE, 0, MPI_DATATYPE_NULL, hostHashs,
+ sizeof(uint64_t), MPI_BYTE, MPI_COMM_WORLD));
+ for (int p=0; p<totalMPIRanksInGlobal; p++) {
+ if (p == MPIRankInGlobal) break;
+ if (hostHashs[p] == hostHashs[MPIRankInGlobal]) MPIRankInLocal++;
+ }
+
+ //std::cout<<"l rank " << MPIRankInLocal << "\n";
+
+ //picking GPUs based on MPIRankInLocal
+ //create cuda stream s
+ s = (cudaStream_t*)malloc(sizeof(cudaStream_t)*nDev);
+ for (int i = 0; i < nDev; ++i) {
+ CUDACHECK(cudaSetDevice(MPIRankInLocal*nDev + i));
Review comment:
line 51and 52 is to set GPUs the current process(MPIRankInLocal) should
control.
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