Getting number of cores (not HT threads)

I have tried sysconf(_SC_NPROCESSORS_ONLN) and sysconf(_SC_NPROCESSORS_CONF), but they both return total number of (as Intel calls it in their CPU documentation) Threads (as in: hyper-threading threads), not physical cores (called Core on mentioned Intel site).

Is there a way to get number of physical cores, instead of logical? Counting entries in /proc/cpuinfo gives 8, similarly to calling sysconf, and my processor is the one linked above.

I'm interested in answers working on Linux and BSDs, preferably in form of C API.

Solution

A different solution is to use hwloc. Here's a simple example:

#include <hwloc.h>
#include <stdio.h>

int main(){

  // Allocate, initialize, and perform topology detection
  hwloc_topology_t topology;
  hwloc_topology_init(&topology);
  hwloc_topology_load(topology);

  // Try to get the number of CPU cores from topology
  int depth = hwloc_get_type_depth(topology, HWLOC_OBJ_CORE);
  if(depth == HWLOC_TYPE_DEPTH_UNKNOWN)
    printf("*** The number of cores is unknown\n");
  else
    printf("*** %u core(s)\n", hwloc_get_nbobjs_by_depth(topology, depth));

  // Destroy topology object and return
  hwloc_topology_destroy(topology);
  return 0;
}

I tested this on a Linux box running Red Hat 4.1.2-48 with GCC 4.1.2, and also on an Apple running OS X 10.8.1 with GCC 4.2.1

Getting number of cores (*not* HT threads)

Getting number of cores (not HT threads)