Newsgroups: comp.parallel.mpi
From: "Umesh Kumar V. Rajasekaran" <urajasek@ececs.uc.edu>
Subject: MPICH on Red Hat Linux, peculiar behaviour
Organization: ECECS Department, University of Cincinnaiti
Date: Fri, 05 Jun 1998 20:15:22 +0000
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Message-ID: <357851D9.646866A2@ececs.uc.edu>

Hi,

    I am using MPICH with ch_p4 on a Red Hat Linux ersion 2.0.33 (gcc version
2.7.2.3).

I wrote a simple ping application where the master sends about 100000 packets of
fixed size to the slave on another machine. I timed the MPI_Send routine, to know how
much time it takes to return back from its call using gettimeofday() system call.
There is no delay between sending successive packets.

I observed a peculiar behaviour. For over 5 MPI_Send calls, 4 of them are taking a
time of about 200-300 microseconds. But the fifth one is taking around 25000
microseconds.

Also another behaviour was that, for message sizes 128, 256, 512, the time of
MPI_Send call is increasing, but after that, for 1024, it suddenly dips around 1/4th
of the other time. and then starts increasing for sizes 2048, 4096.

can someone explain this behaviour.

Thanks in advance
Umesh

--
Umesh Kumar V. Rajasekaran
Department of Electrical and Computer Science and Computer Engineering
University of Cincinnati
email: urajasek@ececs.uc.edu  URL: http://www.ececs.uc.edu/~urajasek/