From 990b2e13182df2c5676d64e7482ad9c10b95c8ce Mon Sep 17 00:00:00 2001 From: josh Date: Wed, 21 Jan 2009 19:54:05 +0000 Subject: [PATCH] updated git-svn-id: svn://anubis/gvsu@376 45c1a28c-8058-47b2-ae61-ca45b979098e --- cs677/hw6/hw.tex | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/cs677/hw6/hw.tex b/cs677/hw6/hw.tex index 7c6f93e..46615ae 100644 --- a/cs677/hw6/hw.tex +++ b/cs677/hw6/hw.tex @@ -62,6 +62,28 @@ they get further from the scattering node. } +\vskip 1em +\item[3.]{ + I wrote an MPI application which incremented a length variable from + 100 to 100000, and then sent and received a message of that length + (the master did a send, then receive, while the slave did a receive + and then a send). + For each length value, I repeated this test 100 times and averaged the + times to get the final round-trip time. + Finally, I took the length value divided by the round-trip time to get + the round-trip bytes per second that could be sent from one MPI host + to another and back again. + I recorded the length that gave the highest round-trip throughput value + and printed that out at the end of the test. + Unfortunately, each time I ran the test the optimal length value + significantly. + Sometimes it printed 6700 or 8400, and sometimes 27000 or 86000. + So, it varied a lot. + I am not sure if this is because once you reach a certain length the + data is simply packed by MPI into the same-sized packets for transfer, + or for some other reason all transfers take about the same amount of + time so it is relatively random which one comes up most efficient. +} \end{enumerate}