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Subject: Re: [hwloc-devel] hwloc_distances as utility?
From: Brice Goglin (Brice.Goglin_at_[hidden])
Date: 2011-07-04 01:13:16


Le 03/07/2011 23:55, Jiri Hladky a écrit :
> Hi all,
>
> I have come across tests/hwloc_distances test and I believe that it
> would be great to convert this into the utility
> "hwloc-report-instances" published under utils/ directory. Please let
> me know what you think about it.
>
> It would take the same input as hwloc-info (read topology from
> different formats instead of discovering the topology on the local
> machine), support both logical and physical indexes (-l and -p) switch.

By the way, lstopo shows distance information, but it does not change it
depending on -l/-p. We may want to fix this.

> I have used stream memory bandwidth benchmark
> (http://www.cs.virginia.edu/stream/) in the past to produce the
> similar output as tests/hwloc_distances. It was interesting to see
> that numactl and kernel scheduler are both using number of hopes
> instead of memory bandwidth.

Actually, Linux only uses the number of hops on one specific MIPS
architecture (SGI IP27 Origin 200/2000). In other cases, it uses the
cpu-to-memory latency (usually reported by ACPI or so).

> On some systems number of hops does not represent memory bandwidth. I
> have reported this in BZ 655041
>
> https://bugzilla.redhat.com/show_bug.cgi?id=655041

This bug is private unfortunately.

> In any case I believe that hwloc-report-instances would be useful
> utility. Please let me know your opinion.

Agreed.

There are still several things to improve regarding distances.
Everything should be in https://svn.open-mpi.org/trac/hwloc/ticket/43

Brice