[Beowulf] Home beowulf - NIC latencies

Joachim Worringen joachim at ccrl-nece.de
Tue Feb 15 04:47:32 EST 2005


Patrick Geoffray wrote:
> For your curiosity, it was using an in-house MPI Pingpong (one message 
> at a time, not a bogus pipelined pingpong used to confuse people and 
> make big pipes look good). For very small messages, most of Pingpong
> codes are similar, 

...but not equal and give different results. Just compare PMB and mpptest.

> compiler has no impact (it was using the gcc that was 
> installed on the machine at that time). 

I experienced differences of more than 2 us depending on whether using 
shared or static libraries, compiler version/options etc. on both scalar 
and vector machines.

 > For asymptotic bandwidth, the
> major difference is the way you compute 1 MB, either 1024*1024 Bytes, or 
> 1000000 Bytes. In the networking world, it tends to be 1000000 Bytes.

I tend to use MB for 10^6 and MiB for 2^10. This is a somewhat official no

  Joachim

-- 
Joachim Worringen - NEC C&C research lab St.Augustin
fon +49-2241-9252.20 - fax .99 - http://www.ccrl-nece.de
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