*nix performance

[Phil Hughes]

In article <4032 at tekgvs.GVS.TEK.COM>, keithe at tekgvs.GVS.TEK.COM (Keith Ericson) writes:
> In article <2733 at ima.ima.isc.com> johnl at ima.UUCP (John R. Levine) writes:

> >On machines with a PC AT bus DMA is rarely a win. It takes so long to get and
> >release the bus that it's faster to...

> We use Micom-Interlan NI5010 network interface boards around here.
> Their instructions indicate NOT to use DMA on an AT-class machine
> because a tight loop doing the data transfers is faster than the
> AT's DMA...

I can't argue with this but personally I like to think I could use
the CPU to do something other than bus reads and writes (even though
some consider this about the limit for an intel chip :-) ).

I have worked on fast mainframes.  Yes, the CPU can do things fast but DMA
I/O was used to free up the CPU.

Anyway, is DMA just slower when I have an idle CPU to do the transfer or
is there something magic that makes the CPU useless while DMA is running?
-- 
Phil Hughes, SSC, Inc. P.O. Box 55549, Seattle, WA 98155  (206)FOR-UNIX
    uw-beaver!tikal!ssc!fyl or uunet!pilchuck!ssc!fyl or attmail!ssc!fyl