Date: Wed, 11 Jan 95 10:26:45 MST From: terry@cs.weber.edu (Terry Lambert) To: bde@zeta.org.au (Bruce Evans) Cc: hsu@cs.hut.fi, wollman@halloran-eldar.lcs.mit.edu, freebsd-hackers@freefall.cdrom.com Subject: Re: FreeBSD as an IP Router Message-ID: <9501111726.AA22967@cs.weber.edu> In-Reply-To: <199501110553.QAA02180@godzilla.zeta.org.au> from "Bruce Evans" at Jan 11, 95 04:53:11 pm
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> >The speed limit for ISA network interfaces is the ISA bus speed. You > >are actually CPU limited, but because the CPU has to reach out over > >the ISA bus to pull data off the interface, it takes much longer than > >would a memory access to data in system RAM. > > Actually, on my DX2/66 with a WD8013EBT (16 bit shared memory), the ISA > overhead for a single interface running `ttcp -t' at full speed is about > 35% while the general system overhead is also about 35%. On slower > systems, the ISA overhead is almost the same while the general system > overhead increases. The system doesn't have to get much slower before > it cannot saturate the ethernet. My DX33 with a WD8013EBT can barely > saturate the ethernet, but when the card is in NE2000 (PIO) mode, it > cannot. I have to agree; the limiting factor is the transport bandwidth, since it is less than the bus bandwidth. I can prove this by running a Novell NetWare sever on a split vs. a single net (2 cards vs. 1) with 125 clients on either net -- and have done so in Novell's SuperLab. Whether the drivers are too compute intensive to make this work well is another question (the FreeBSD drivers are not, the UnixWare drivers are borderline above the 250 client range due to [unidentified] propagation latencies in the Streams implementation). By the way, judging Streams by USL's implementation is equivalent to judging rock music by Primus. 8^). Terry Lambert terry@cs.weber.edu --- Any opinions in this posting are my own and not those of my present or previous employers.
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