[lug] It slows down

[David]

Today I managed to capture some data on an intermittently occurring
problem.  The problem is something that I have always realised I could
be imagining; but today I measured convincing evidence that sometimes
something strange happens to my machine.  I am reporting it in case
anyone else has seen something similar, or knows about it, etc.
Unfortunately, I do not have nearly enough data to deduce any
conclusion with confidence; and intentionally doing experiments has
been perceived as too much of a time imposition, at least up until
now.

As a starting point I shall describe the problem as a significant
slowing down of my machine from some moment in time.  Once the
computer has "switched" into this mode everything takes much longer to
run: I get spurious pauses, delays, and slow performance.  The datum I
captured today is that, after the computer started to run slowly, a
computationally intensive programme of mine took 7446 seconds to run.
After this run had completed, I did a soft boot, and re-ran the
programme without changing any data, i.e., an identical run from my
point of view - it took 2607 seconds.

There are many more questions than answers here.  All I can do is
itemise what may be relevant points.

* Currently I am running KRUD/RH7.0; but I have seen this problem
  without KRUD and with earlier versions of RedHat.

* Normally I shut-down and turn-off my computer at night and re-boot
  in the morning.  This was the case today.

* Pentium II, 200mHz, 128mB, IDE discs
aside: I bought an AMD 1.4gHz, 0.5gB, 7200rpm machine today, which I
pick up tomorrow; whoopee-do, I am hoping that my life is about to
take off!

* Today was typical, I ran several copies of Emacs, three copies of
  xdvi, netscape, and several xterms.  I used a calculator briefly.

* It is possible that the slowdown always occurs when the machine has
  several, say ten, of these processes running simultaneously.

* It is possible that the slowdown occurs during use of netscape.

* Once the machine has flipped into go-slow mode it will not come out
  of it just by killing processes; I am 90% sure of this, and I shall
  monitor this more carefully in the future.

* There is no rogue process that I have detected by using ps.

* Could this problem be caused by swapping?  Note that when I start
  one of these jobs I go away and do something else since I need the
  results of one run to decide what to do next.  So, as far as I know,
  there is nothing competing for cycles and no need for swapping.
  Even if I do not go away normally all I do is edit text or something
  else fairly benign.  Even if I compile something else, the
  consequent slow down of the two processes has a different feel to it
  than "the problem"; and, of course, the slow down goes away when one
  of the processes finishes.

* Is the problem in:

+ the hardware?

+ Netscape?  I am suspicious of this, but I just do not know if I am
  always running netscape when the flip occurs.  I shall monitor this
  in the future.

+ Java applets emitted from netscape?

+ Emacs?  That would be a real find!!

+ My code.  Well, this is a good question.  But I get different times
  with identical runs.  I am biased, of course, but I doubt that this
  is it.

+ Window manager, fvwm.  This and netscape are my favorite suspects.

+ Linux?  It could be...


Pretty weird, vague as well, I know.  However, it is fairly clear that
something is being started, somehow, that eats cycles voraciously; and
the lack of a rogue process (is there a better way to check than using
ps?) points to an existing process going haywire.

So, this description is just for the record.  But if you have seen
anything like this, then I. for one, will be interested to hear about
it.