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[linrad] Re: Linrad, ps aux numbers, etc

Hillo, Kohjin!

Welcome to the world of Linrad!

If you look at the bottom left of the Linrad screen, Leif has provided a
'%time' readout.  Leif notes that this parameter indicates "% of the
time available for processing within the dsp program".  On my system
running with a 96000 Hz sampling rate and a 90+ KHz wide waterfall, with
very aggressive parameters, this % time is (while sampling one of the
famous FRH files) 28.3%.  It is a good index of what happens to
processor load as you change parameters.

If you use 'ps aux' or 'ps ux' etc you will get vastly different numbers
than this, as you have discovered.  When I run 'ps aux' or 'ps ux' or
whatever from another terminal, the Linrad numbers generally run at 98
or 99% for %cpu.  This is with a pentium 4 running at 1.4 GHZ.  

By the way, I find it more convenient to run 'top' rather than 'ps aux'
repeatedly from another terminal to determine what Linrad or any other
process is doing on an ongoing basis.  'Top' continuously updates in
realtime (and the update interval can be adjusted), and provides a lot
more useful info than Ps aux does without having to enter a lot of
options after the command on the command line.  Note however that 'Top'
itself shows a lot of cpu usage on startup, but then it drops off to
very low values.  This is an 'artifact' of the calculation method used
on the first iteration, I believe.  To run 'top' just type 'top' on the
command line.  No options, etc are needed, although there are plenty of
options if you want to use them.

In spite of the 'ps' or 'top' numbers for CPU usage, my P4 1.4GHz has NO
problem keeping up with Linrad even with a bunch of other stuff (88
processes) running in the background.  So I wouldn't worry about the CPU
number unless you are having trouble.  It's like Parkinson's Law; the
work expands to fill the time available to it ;)

BY the way, I run with MMx and SIMD instructions.  If you are interested
in a complete list of the parameters I am running, let me know and I'll
email them to you.  

> Well, I found the CPU load remains almost same (heavy) as it's running

> during set up window. In other words, about CPU load of 80% doesn't 
> change in running phase nor setup phase. This load slowly increases 
> from about 70% at the startup up to more than 90% finally.

For the 'ps' or 'top' numbers this is true.  Is the CPU load actually
causing you a problem?  I have been running Linrad since February 2001
and have not had ANY problems in this regard, even at dual polarity
96000 sampling rate with both noiseblankers running, AFC on, SPUR
cancellation, etc. etc.  That is with the exception not of a Linrad
problem, but with another task that CRON was running coming in and
stealing lots of CPU time.  This disturbed Linrad or whatever else was
running.  So I disabled the CRON nonsense, and the problem was cured.  I
admit that my processor is faster than the one you are using, but my
message holds even so.  If you are not having an actual performance
problem that interferes with your use of Linrad, don't worry about the
CPU usage numbers on 'ps' or 'top'.  Linrad is not meant to run in the
background, and you really shouldn't be running a lot of CPU intensive
processes while its running since it takes up the whole terminal display
anyway, and most of the background stuff in Linux uses very little CPU

I'd suggest that if you want to see how your parameter choices affect
your timing, use the '%time' number that Leif kindly provided on the
screen rather than 'ps' or 'top'.  Leif's number will show you how your
choices affect processing times.  If you want more information, type 't'
when you have the waterfall display, etc running in Linrad and you will
have much more information than you want ;)  It will also be in the
bottom left corner of the screen.  You can 'zero' or restart the display
by typing 'z'.

I hope that helps.  Let me know if there are any questions or


Roger Rehr
W3SZ   FN20ah
2 Merrymount Road
Reading, PA  19609-1718