Changes between Version 5 and Version 6 of SourceCode/Performances/Bench_May2016


Ignore:
Timestamp:
2016-05-25T18:34:04+02:00 (8 years ago)
Author:
jpolcher
Comment:

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  • SourceCode/Performances/Bench_May2016

    v5 v6  
    1212|| Size of history file  || 41M               || 225M || 
    1313 
    14 The version of the model used is the last version of ORCHIDEE-DRIVER before the merge (May 2016) 
     14The version of the model used is the last version of ORCHIDEE-DRIVER before the merge (May 2016). The same version and configuration of the model is used and only the way the forcing data (radiation fluxes, atmospheric conditions and precipitation types) is provided to ORCHIDEE differ. 
    1515 
    1616The IO was configured to minimise the output but still using IOIPSL. The size of the output files are given in the table above. 
    … …  
    3030 
    3131== Results == 
     32 
     33The three drivers benched here can be characterised as follows : 
     34- Old driver : In this historical driver all CPUs access the netCDF file which contains the forcing data, does the time interpolation and provides it to ORCHIDEE 
     35- New driver : Only the root processor reads the data and this only at the beginning of the simulation. Then each processor gets its fraction of the grid points and does the temporal interpolation before passing it to ORCHIDEE. 
     36- OASIS driver : This is a totally different approach where one processor is dedicated to reading the forcing data and doing the time interpolation. The OASIS is then used to distribute the data at each time step (every 900 seconds) to the n-1 processors which run ORCHIDEE.  
     37 
     38The new driver and the OASIS mode contain much more complex time interpolations. This can generate more operations and thus need more CPU time. 
    3239 
    3340=== Real Time === 
    … …  
    5259[[Image(Bench_ORCHIDEE-3.png, width=40%)]] 
    5360 
    54 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. 
     61It shows that the better speed-up is achieved by the new driver. To understand this one has to remember that the new driver will read the forcing only 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 and thus generate more system calls. 
    5562 
    56 Two indices show that this can explain the better speed-up for the new driver. 
     63Two indices show that this can explain the better speed-up of the new driver. 
    5764 
    5865[[Image(Bench_ORCHIDEE-5.png, width=40%)]] 
    … …  
    6067The 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. 
    6168 
    62 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. 
     69Another hint to the slow down caused by multiple processors accessing the same netCDF file for the forcing can be seen in the system time returned by UNIX's time command. 
    6370 
    6471[[Image(Bench_ORCHIDEE-2.png, width=40%)]]