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From: Lisandro Dalcin (dalcinl_at_[hidden])
Date: 2006-10-23 18:05:17


On 10/23/06, Tony Ladd <ladd_at_[hidden]> wrote:
> A couple of comments regarding issues raised by this thread.
>
> 1) In my opinion Netpipe is not such a great network benchmarking tool for
> HPC applications. It measures timings based on the completion of the send
> call on the transmitter not the completion of the receive. Thus, if there is
> a delay in copying the send buffer across the net, it will report a
> misleading timing compared with the wall-clock time. This is particularly
> problematic with multiple pairs of edge exchanges, which can oversubscribe
> most GigE switches. Here the netpipe timings can be off by orders of
> magnitude compared with the wall clock. The good thing about writing your
> own code is that you know what it has done (of course no one else knows,
> which can be a problem). But it seems many people are unaware of the timing
> issue in Netpipe.

Yes! I've noticed that. I am now using Intel MPI Benchmarck. PingPong
/PingPing and SendRecv test cases seems to be more realistic. Does any
one have any comments about this test suite?

> 2) Its worth distinguishing between ethernet and TCP/IP. With MPIGAMMA, the
> Intel Pro 1000 NIC has a latency of 12 microsecs including the switch and a
> duplex bandwidth of 220 MBytes/sec. With the Extreme Networks X450a-48t
> switch we can sustain 220MBytes/sec over 48 ports at once. This is not IB
> performance but it seems sufficient to scale a number of applications to the
> 100 cpu level, and perhaps beyond.
>

GAMMA seems to be a great work, looking at some of its reports in web
site. Hoever, I have not tried it yet, and I am not sure if I will,
mainly because only supports MPICH-1. Has anyone any rough idea how
much work it could be to make it availabe for OpenMPI. Seems to be a
very interesting student project...

-- 
Lisandro Dalcín
---------------
Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
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