Peter Koch sez:

 > > 3. NetBSD-1.3 is WAY slower on the Mac than on a Sun3. My IIvx
 > >    does have a 68030 at 33 MHz and 8 MB of memory, but my two
 > >    Sun3's (one 68030 at 24 MHz, one 68020 at 20 MHz) are MUCH
 > >    more zippier. Ok, they have 12 MB of memory, but does this
 > >    explain such a vast slowdown?
 > >    Or is the Mac hardware THAT BAD?
 > >    I can't believe my benchmark results... The Mac is slower,
 > >    even on CPU-intensive jobs?!?

There are several factors that can come into play, here.  One of the
biggest ones is, believe it or not, SCSI performance.  When you run
a program, it is not loaded into memory... it is loaded from disk
on-demand (as you access the program's memory pages).  If your SCSI
performance is low, this is going to take longer, making the system
appear slower.  Believe it or not, the SCSI on a Sun 3 is really pretty
decent (an NCR 5380 with a DMA engine in front of it; the Mac has no
DMA engine on almost all models).

The Mac also has a screwy interrupt scheme, which places clock interrupts
below other interrupts.  This means that if other devices are interrupting
frequently, you can be blocking the clock.  The clock interrupt is what
drives process scheduling; blocking the clock interrupt for long periods
can cause runnable processes to not get run in a timely fashion.  It can
also skew the real time clock (Let's do the time warp again! :-)

Also, memory really can have a substantial effect on system performance.
If you have a CPU intensive benchmark, which requires a large working set,
and you can fit that working set into RAM, you're going to be in for
trouble.  (And, when the system begins paging things out to the swap
area, the fact that the Mac has no SCSI DMA engine is going to be
painfully obvious :-)  You really are better off getting more RAM before
a faster CPU, in many cases.

Jason R. Thorpe                                       thorpej@nas.nasa.gov
NASA Ames Research Center                            Home: +1 408 866 1912
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