Vax 11/780 performance vs Sun 4/280 performance

[Jon Olson]

> What your DEC salesperson may have heard, undoubtedly very indirectly, is that
> there is a knee in the performance curve of the Sun-4/280 at > 15 processes
> ready-to-run.  This has nothing to do with > 15 users: more like a load average
> of > 15.  Do your vaxes ever run with a load average of > 15?  If not, ok.  But,
> if they EVER hit 16 or 17, watch out on the Sun-4's:  I can trivially get my
> Sun-4 completely wedged so I have to reboot with L1-A by just starting 19 little
> processes which sleep for 100ms, wake-up and sleep again.  This doesn't even
> raise the load average (but amounts to a load average of 19 to the context
> switching mechanism, although not to the cpu).
> 
> And the Sun-3's are no better: the knee there is >7 processes.
> 
> -mark

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 );
  }

-- 
Jon Olson, Modular Mining Systems
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-- 
Jon Olson, Modular Mining Systems
USENET:     {ihnp4,allegra,cmcl2,hao!noao}!arizona!modular!olson
INTERNET:   modular!olson at arizona.edu