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8
PERFORMANCE
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indicate considerable idle time. It is more important to keep the atm and ocean processors busy as the
number of processors assigned to atm and ocean is much larger than the number assigned to ice and
land.
The script getTiming.csh, in the directory $CCSMROOT/scripts/ccsm utils/Tools/getTiming, can be
used to aid in the collection of run time statistics needed to examine the load balance efficiency.
The following examples illustrate some issues involved in load balancing a CCSM3 run for a T42 gx1v3
run on bluesky.
Case
LB1
LB2
====================================
OCN cpus
40
48
ATM cpus
32
40
ICE cpus
16
20
LND cpus
8
12
CPL cpus
8
8
total CPUs
104
128
stepon
336
280
node seconds
34944
35840
simulated yrs/day
7.05
8.45
simulated yrs/day/cpu .067
.066
In the above example, adding more processors in the correct balance resulted in an ensemble that
was ”faster” (computed more years per wall clock day) and statistically just as efficient (years per day
per cpu). The example below shows that assigning more processors to a given run may speed up that
run (generates more simulated years per day) but may be less processor efficient.
Case
LB3
LB4
====================================
OCN cpus
32
48
ATM cpus
16
40
ICE cpus
8
20
LND cpus
4
12
CPL cpus
4
8
total CPUs
64
128
stepon
471
280
node seconds
30144 35840
simulated yrs/day
5.03
8.45
simulated yrs/day/cpu .078
.066
Learning how to analyze run time statistics and properly assign processors to components takes
considerable time and is beyond the scope of this document.