On 11/12/10 02:56 PM, Simon King wrote:
Hi!
On certain machines, I encounter the problem that the wall time for my
computations is *much* more than the CPU time. For example, on one
machine, the CPU time is 60 minutes, but the wall time is 330 minutes.
On a different machine, the CPU time is 13 minutes but the wall time
19 minutes.
So, on some machine the wall/CPU ratio is greater than 5, on another
machine it is less than 2 - for the same computation.
My uneducated guess is that this is due to I/O processes: They do not
count for the CPU time, but are of course relevant for the wall time,
and the time spent depends on the machine.
Of course I want to improve the situation. So, I'd like to find out
what parts of my programs are causing the high ratio. Do you know of
any profiling tools available in Sage that are suitable for analysing
I/O processes (or other processes that may explain the wall/CPU
ratio)?
Cheers,
Simon
Sage is the place to look - use tools supplied with the operating system.
I know on Solaris, I'd be looking at the output of vmstat. That will list a
number of parameters.
Memory exhausion is one possibility. In that case, on Solaris at least, the scan
rate (sr column) would be non-zero, indicting pages are being swapped out of
memory onto disk.
sar is another tool worth looking at.
Unfortunately, interpreting the output of vmstat and sar is non-trivial, but I'm
sure you can find web resources to help you.
Dave
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