Changes between Version 4 and Version 5 of SourceCode/Performances/Bench_May2016

Timestamp:

2016-05-25T18:20:32+02:00 (8 years ago)

Author:

jpolcher

Comment:

--

SourceCode/Performances/Bench_May2016

@@ -52 +52 @@
 [[Image(Bench_ORCHIDEE-3.png, width=40%)]]
 
+It shows that the better speed-up is achieved by the new driver. To understand one has to know that the new driver will read the forcing on one processor and then scatters the information to the other processors using MPI. In the old driver all processors read the netCDF file in order to obtain the data needed.
 
+Two indices show that this can explain the better speed-up for the new driver.
+
+[[Image(Bench_ORCHIDEE-5.png, width=40%)]]
+
+The above figure displays the CPU time taken by MPI. It is clear that as the number of CPUs increases in the new driver more time is spent in the data transfer. I this graphic the OASIS driver does not count MPI exchanges needed for the forcing data as it is part of OASIS and not ORCHIDEE.
+
+Another hint to the slow down by multiple processors accessing the same netCDF file for the forcing can be seen in the system time returned by UNIX's time command.
+
+[[Image(Bench_ORCHIDEE-2.png, width=40%)]]
+
+As we increase the number of CPUs in the old driver, the system time increases while in the new driver this time remains flat.
+
+