From: Jim Tuccillo <jjt@radia1.com>
Newsgroups: comp.parallel.mpi
Subject: Re: latency and bandwidth on IBM SP2
Date: Tue, 08 Sep 1998 09:48:04 -0400
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Hi Jorgen,

   I have not observed this sort of behavior. Please post the code you
are using and the node type. Are you sure the system was being used only
by yourself ?

Regards,
  Jim

Jorgen Moth wrote:
> 
> Hi
> I am measuring the latency (software latency) using non-blocking mpi_isend
> on IBM SP2 with high-performance-switch. However my measurements (taken by
> the built in rtc() real time clock routine from fortran) seems to indicate
> that there is some copying going on from the user's buffer area to an
> internal hidden buffer. I would expect an message-length-independent latency
> (time from calling mpi_isend until control is returned to my fortran
> program) round about 20-30 usec, however the time varies according to the
> length of the message to be sent, i.e. several hundred useconds for 10 kB
> messages. Does anybody (IBM?) want to commment?
> Also, has anybody had experience or being using the basic driver routines
> for the high-performance-switch (ccs0?).
> 
> Regards
> Jorgen Moth
> UNI-C, The Danish Computing Centre for Research and Education
> jorgen.moth@uni-c.dk