MS-312 Set openmp thread number by config

Former-commit-id: 7ddafa3aa22d0455b343d07cc37b1a30d1ac29a1

cpp/conf/server_config.template

@@ -44,4 +44,4 @@ engine_config:
   nlist: 16384
   use_blas_threshold: 20
   metric_type: L2               # compare vectors by euclidean distance(L2) or inner product(IP), optional: L2 or IP
-  omp_thread_occupancy: 0.75    # how many compute threads be used, this is a percent value compare to system cpu core number(for instance: cpu core is 4, then 0.75 means use 3 compute threads)
+  omp_thread_num: 0             # how many compute threads be used by engine, 0 means use all cpu core to compute

cpp/src/server/DBWrapper.cpp

@@ -62,13 +62,11 @@ DBWrapper::DBWrapper() {
 
     // engine config
     ConfigNode& engine_config = ServerConfig::GetInstance().GetConfig(CONFIG_ENGINE);
-    float omp_thread_rate = engine_config.GetFloatValue(CONFIG_OMP_THREAD_RATE, 0.75);
-    uint32_t cpu_count = 1;
-    CommonUtil::GetSystemAvailableThreads(cpu_count);
-    float thread_count = omp_thread_rate*(float)cpu_count;
-    int32_t omp_thread = (int32_t)round(thread_count);
-    omp_set_num_threads(omp_thread);
-    SERVER_LOG_DEBUG << "Openmp thread number = " << omp_thread;
+    int32_t omp_thread = engine_config.GetInt32Value(CONFIG_OMP_THREAD_NUM, 0);
+    if(omp_thread > 0) {
+        omp_set_num_threads(omp_thread);
+        SERVER_LOG_DEBUG << "Specify openmp thread number: " << omp_thread;
+    }
 
     //set archive config
     engine::ArchiveConf::CriteriaT criterial;

cpp/src/server/ServerConfig.h

@@ -53,7 +53,7 @@ static const std::string CONFIG_NPROBE = "nprobe";
 static const std::string CONFIG_NLIST = "nlist";
 static const std::string CONFIG_DCBT = "use_blas_threshold";
 static const std::string CONFIG_METRICTYPE = "metric_type";
-static const std::string CONFIG_OMP_THREAD_RATE = "omp_thread_occupancy";
+static const std::string CONFIG_OMP_THREAD_NUM = "omp_thread_num";
 
 class ServerConfig {
  public: