hwloc (Hardware Locality)

The following C example demonstrates how to initialize a topology, walk the tree, count packages, calculate cache sizes, and perform CPU and memory binding. This example is based on doc/examples/hwloc-hello.c.

/*
* Example hwloc API program.
* See other examples under doc/examples/ in the source tree
*/
#include "hwloc.h"
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

static void print_children(hwloc_topology_t topology, hwloc_obj_t obj, int depth)
{
    char type[32], attr[1024];
    unsigned i;
    hwloc_obj_type_snprintf(type, sizeof(type), obj, 0, topology);
    printf("%*s%s", 2*depth, "", type);
    if (obj->os_index != (unsigned) -1)
        printf("#%u", obj->os_index);
    hwloc_obj_attr_snprintf(attr, sizeof(attr), obj, " ", 0, topology);
    if (*attr)
        printf("(%s)", attr);
    printf("\n");
    for (i = 0; i < obj->arity; i++) {
        print_children(topology, obj->children[i], depth + 1);
    }
}

int main(void)
{
    int depth;
    unsigned i, n;
    unsigned long size;
    int levels;
    char string[128];
    int topodepth;
    void *m;
    hwloc_topology_t topology;
    hwloc_cpuset_t cpuset;
    hwloc_obj_t obj;

    /* Allocate and initialize topology object. */
    hwloc_topology_init(&topology);

    /* Perform the topology detection. */
    hwloc_topology_load(topology);

    /* Get topology depth. */
    topodepth = hwloc_topology_get_depth(topology);

    /*****************************************************************
    * First example: Walk the topology with an array style
    *****************************************************************/
    for (depth = 0; depth < topodepth; depth++) {
        printf("*** Objects at level %d\n", depth);
        for (i = 0; i < hwloc_get_nbobjs_by_depth(topology, depth); i++) {
            hwloc_obj_type_snprintf(string, sizeof(string), 
                                    hwloc_get_obj_by_depth(topology, depth, i), 
                                    0, topology);
            printf("Index %u: %s\n", i, string);
        }
    }

    /*****************************************************************
    * Second example: Walk the topology with a tree style
    *****************************************************************/
    printf("*** Printing overall tree\n");
    print_children(topology, hwloc_get_root_obj(topology), 0);

    /*****************************************************************
    * Third example: Print the number of packages
    *****************************************************************/
    depth = hwloc_get_type_depth(topology, HWLOC_OBJ_PACKAGE);
    if (depth == HWLOC_TYPE_DEPTH_UNKNOWN) {
        printf("*** The number of packages is unknown\n");
    } else {
        printf("*** %u package(s)\n", hwloc_get_nbobjs_by_depth(topology, depth));
    }

    /*****************************************************************
    * Fourth example: Compute cache size above the first logical processor
    *****************************************************************/
    levels = 0;
    size = 0;
    for (obj = hwloc_get_obj_by_type(topology, HWLOC_OBJ_PU, 0); obj; obj = obj->parent)
        if (hwloc_obj_type_is_cache(obj->type)) {
            levels++;
            size += obj->attr->cache.size;
        }
    printf("*** Logical processor 0 has %d caches totaling %luKB\n", levels, size / 1024);

    /*****************************************************************
    * Fifth example: Bind to only one thread of the last core
    *****************************************************************/
    depth = hwloc_get_type_or_below_depth(topology, HWLOC_OBJ_CORE);
    obj = hwloc_get_obj_by_depth(topology, depth, hwloc_get_nbobjs_by_depth(topology, depth) - 1);
    if (obj) {
        cpuset = hwloc_bitmap_dup(obj->cpuset);
        hwloc_bitmap_singlify(cpuset);
        if (hwloc_set_cpubind(topology, cpuset, 0)) {
            char *str;
            int error = errno;
            hwloc_bitmap_asprintf(&str, obj->cpuset);
            printf("Couldn't bind to cpuset %s: %s\n", str, strerror(error));
            free(str);
        }
        hwloc_bitmap_free(cpuset);
    }

    /*****************************************************************
    * Sixth example: Memory binding on the last NUMA node
    *****************************************************************/
    n = hwloc_get_nbobjs_by_type(topology, HWLOC_OBJ_NUMANODE);
    obj = hwloc_get_obj_by_type(topology, HWLOC_OBJ_NUMANODE, n - 1);
    size = 1024*1024;
    m = hwloc_alloc_membind(topology, size, obj->nodeset, HWLOC_MEMBIND_BIND, HWLOC_MEMBIND_BYNODESET);
    hwloc_free(topology, m, size);

    m = malloc(size);
    hwloc_set_area_membind(topology, m, size, obj->nodeset, HWLOC_MEMBIND_BIND, HWLOC_MEMBIND_BYNODESET);
    free(m);

    /* Destroy topology object. */
    hwloc_topology_destroy(topology);
    return 0;
}