Vax 11/780 performance vs Sun 4/280 performance

[weiser.pa at xerox.com]

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Nonsense, I just tried forking 32 copies of the following program
on my Sun 3/60 workstation.  Each one sleeps for 100 milliseconds,
wakes up, and sleeps again.  With 32 copies of it running, I could
notice no difference in response time and a `ps aux' showed none
of them using a significant amount of CPU time.  Maybe you are just
running out of memory and doing alot of swapping?

What I have noticed on our Vax 11/780, running VMS, is that it is
often equally slow with 1 user or 20 users.  Possibly VMS avoids the
`knee' by raising the priority of the NULL task when there aren't many
people on the machine???

#include <sys/time.h>

main()
  {
  struct timeval tv;

  tv.tv_sec = 0;
  tv.tv_usec = 100000;
  for( ;; )
    select( 0, 0, 0, 0, &tv );
  }

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No, not nonsense.  I changed 100000 to 25000, and ran 18 of these on my
Sun-4/260 with 120MB swap and 24MB ram, with very little else going on.
Perfmeter shows no disk activity, ps aux shows each of the 18 using almost no
cpu.  (And each of the 18 has more than millisecond to get in and out of select,
which is certainly enough).  And the system is to its knees!  (If it doesn't
work for you, try 19 or 20 or 21).  Window refreshes take 10's of seconds.  If I
kill off 3 of these, all is back to normal.

I don't have a 60C to try this on.  But, try reducing that delay factor and see
if you don't also see a knee in the performance curve well before the cpu should
be swamped.  (And in any case, swamped cpu doesn't need to imply knee in the
curve...)

-mark