jdc@rama.UUCP (James D. Cronin) (07/27/88)
Do any of you netlanders know what the paging performance is for
Vaxen (or any other machine, for that matter)? For example, how
long does it take to service a "soft" page fault (i.e. the desired
page is in the free/modified page list) vs. a "hard" page fault
(i.e. going out to disk).
Thanks in advance,
Jim Cronin
--
James D. Cronin UUCP: {...}!rochester!tropix!rama!jdc
Scientific Calculations/Harrispardo@june.cs.washington.edu (David Keppel) (07/30/88)
>[ Faulting performance on a VAX ]
You can probably figure it out yourself by setting your csh "time"
variable with:
set time=(5 "%Uu %Ss %E %P (%Xt+%Dds+%Kavg+%Mmax)k %Ii+%Oo (%Fmaj+%Rmin)pf %Wswaps")
The "maj" figure is "major", or i/o-requiring faults, while "min" is
"minor", or recoverable faults. The "k" figures are wrong in various
combinations on various machines (bugs in undocumented features) so
don't use them. "u"=user time, "s"=system time, %E is for elapsed
time, and %P is percent of cpu (computed as [s+u]/elapsed).
Page fault times are idle/faults, and idle time is elapsed-(s+u).
Now all you need to do is find a machine where you can allocate more
virtual memory than physical memory (not always easy) and write some
programs that have various kinds of faulting behavior. One way to do
this is to allocate a huge array (larger than physical memory) and
step through it in page-size increments. You can compare performance
when the pages are only read, when they are written, etc.
As you get below the physical memory limit the hard fault rate should
drop dramatically. Soft faults are harder to generate so you may need
to do some algebra to figure out soft rates once you know the hard
rates.
Your tests should probably be done on a lightly-loaded system else
your process will be ready to go after a page fault but will not run
because the CPU is busy.
;-D on ( followup reply e-mail, avoid posts! ) Pardoshepperd@dms.UUCP (Dave Shepperd) (08/02/88)
From article <8103@rama.UUCP>, by jdc@rama.UUCP (James D. Cronin): > > > Do any of you netlanders know what the paging performance is for > Vaxen (or any other machine, for that matter)? For example, how > long does it take to service a "soft" page fault (i.e. the desired > page is in the free/modified page list) vs. a "hard" page fault > (i.e. going out to disk). Measured softfault times: Vax 11/730 1700 Vax 11/750 800 Vax 11/780 500 uVax II 500 Vax 3xxx 180 All times in microseconds and are reasonably accurate. The one I remember for sure is the the 11/780 at 498us. The 730 and 750 were measured with VMS 3.x. The 780 was measured under VMS 3.x and VMS 4.x (no difference). The uVax II and Vax 3xxx were measured under VMS 4.7. Hard fault times are a function of your paging disk's specs coupled with what other I/O demands your system is placing on it.