[daip] (no subject)

[Eric Greisen]

chenxi writes:

 >    I have one question about AIPS task. Why the process of some tasks of 31DEC02 version, e.g. "possm", "split", is very slow in my computer (Redheat 8.0, CPU 2.4). While for the same data, these processes are relatively quick in other computer with same configure. 
 >   Can you give me the explain for them? Thank you!	
 > 

First - please always give a subject line.  I am amazed that I noticed
your e-mail and checked it among the dozens of SPAMs I was skipping
over.

Your question is hard to answer without more information.  One thing
that always slows tasks down is the disk configuration.  If you are
using disk areas that are actually on another computer, then the disk
I/O must go through Network File System.   That works, but it has to
do exactly what you tell it to do - i.e. open a file, read/write a
record, close a file.  On your own Linux computer, the operating
system will not actually update the disk until it is convenient,
keeping much of disk files in memory which is very fast compared to
disk.  When the message file is over NFS, we measured 1 second real
time per message (probably faster now) compared to essentially no time
at all per message on a local message file.  That is a worst case, but
indicative.

Other things that can slow you down are multiple tasks running at the
same time competing for the CPU and disk.  If the load modules are
coming from a file server rather than the local host, this can slow
things also, although that effect is usually not important.

If your computer has too little real memory (e.g. 256 Mbytes) for
whatever else you are running in the machine (emacs, mozilla, etc use
large amounts of virtual memory), then swapping may slow you down.  If
the swap disk area is too small or on the same disk drive as an aips
data area, then this disk conflict may also retard performance.

Thise are some general thoughts, but may not apply.

Consider updating to 31DEC05:
    http://www.aoc.nrao.edu/aips/
although that will not help the performance issue.

Eric Greisen