25 Feb
2003
25 Feb
'03
5:36 a.m.
On Tue, 25 Feb 2003, Zane H. Healy wrote:
Does the FDDI controller load down the host systems
CPU, or does it handle
the load onboard? It doesn't really matter, after a little research, I
don't think I'll be testing this unless I happen upon a really cheap FDDI
controller, it looks like they're more than I can afford to spend on a
something that would be to simply satisfy my curiousity.
I'd imagine that if you saturate the Qbus with traffic over the FDDI
module, you'll probably cause some pain for any other peripherals which
also rely on the Qbus. I think most of the Qbus gear tends to be very
good about offloading I/O processing to the boards themselves, but I'd
still expect the CPU to take a hit for things like assembling and
disassembling the TCP/IP packets (calculating checksums and moving bits
around kernel and user buffer areas.) If you're running diskless off
NFS, I'd expecting more CPU requirements associated with all the
filesystem overhead. Still, I'd imagine it'd be quite a lot faster
than locally attached MFM disks.
I can't claim to be much of an expert on the internals of the NetBSD
kernel, or on the capabilities of the DEFQA, but I wouldn't be surprised
if the CPU on something like a MicroVAX-II ended up being the weakest
link in pushing data over FDDI. It'd be interesting to gather some
empirical data for something like MicroVAX-II, MicroVAX 3600, and
various VAX 4000 models.
-brian.