Date: Wed, 11 Jan 1995 16:53:11 +1100 From: Bruce Evans <bde@zeta.org.au> To: hsu@cs.hut.fi, wollman@halloran-eldar.lcs.mit.edu Cc: freebsd-hackers@freefall.cdrom.com Subject: Re: FreeBSD as an IP Router Message-ID: <199501110553.QAA02180@godzilla.zeta.org.au>
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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. Bruce
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