Improving ADF performance on supercomputers
In some cases you may find that ADF is wasting time waiting for I/O.
A large difference between Elapsed time and CPU time indicates
that this is happening.
The reason is typically that:
- ADF is sharing an I/O system with
another application that uses I/O heavily
- the I/O bandwidth
of the system is insufficient.
In such a case, if your machine has enough memory, you can make
sure that ADF keeps its files (partially) in memory. In this way,
I/O and
the corresponding delays are kept to a minimum.
Problem
You notice for your ADF job that there is a gap between the
Elapsed time and CPU time. These are printed by ADF near the
end of your output file. This delay may well be (partially)
due to the fact that the program is waiting for I/O.
Solution
Increase the value for the SCM_IOBUFFERSIZE environment variable.
I/O can be avoided completely in this manner if you have enough
memory available. If your system has 1 GB of memory per CPU,
128 or 256 are reasonable values for SCM_IOBUFFERSIZE.
These numbers refer to the number of MBytes per CPU reserved
for I/O buffering.
Lengthy E-mail from SCM on this topic
