updated

git-svn-id: svn://anubis/gvsu@376 45c1a28c-8058-47b2-ae61-ca45b979098e

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}