I would add that the hwloc_distances_s returned by
hwloc_get_whole_distance_matrix_by_depth(topology, 0) is: { 0, 0, 0x0, 0, 0 }
On Aug 6, 2012, at 3:47 PM, Wheeler, Kyle Bruce wrote:
> Hello,
>
> I'm failing to understand what hwloc (v1.5) is doing. I'm trying to use
> hwloc_get_latency() to determine the distance between two cores.
>
> The two cores are on different sockets. According to libnuma's numactl, the
> latency between the two sockets is 20, whereas between cores on the same
> socket is 10. According to hwloc-ls -v, the latency is 2.0, whereas between
> cores on the same socket is 1.0. Thus, I know that hwloc is getting topology
> information.
>
> However, programmatically, hwloc_get_latency() just returns -1. I tried using
> hwloc_get_whole_distance_matrix_by_depth(), and found that the distance
> matrix is only defined for depth 0, which, according to
> hwloc_obj_type_string(hwloc_get_depth_type(topology, 0)) is "Machine". Now,
> the documentation for hwloc_get_whole_distance_matrix_by_depth() says it
> returns "a distances structure containing a matrix with all distances between
> all objects at the given depth". Given that I only have one object that depth
> 0 (just the one machine), what does this mean? If I try with depth 1 (aka
> "NUMANode" or HWLOC_OBJ_NODE), I get NULL back, suggesting that there is no
> matrix of distances between NUMANodes. Of course, that's not true; hwloc-ls
> reports that matrix! So what's going on here?
>
> And why is hwloc_get_latency() failing?
> --
> Kyle B. Wheeler
> Dept. 1423: Scalable System Software
> Sandia National Laboratories
> 505-844-0394
>
>
>
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>
--
Kyle B. Wheeler
Dept. 1423: Scalable System Software
Sandia National Laboratories
505-844-0394
