*BSD News Article 83084


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From: raj@cup.hp.com (Rick Jones)
Newsgroups: comp.unix.bsd.freebsd.misc,comp.unix.bsd.misc
Subject: Re: 100Base-TX: where's the bottleneck?
Followup-To: comp.unix.bsd.freebsd.misc,comp.unix.bsd.misc
Date: 16 Nov 1996 02:28:06 GMT
Organization: Hewlett-Packard's Network Computing Division
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Matt Dillon (dillon@flea.best.net) wrote:
:     This sort of thing is where PCI DMA really starts to show its suds
:     as compared to ISA.  You actually *could* drive a gigabit ethernet
:     (100 MBytes/sec = 1000 MBits/sec) via PCI, though it wouldn't leave
:     much room for anything else.  Still, with a DMA based driver and
:     a pentium pro > 150 MHz, there would possibly even be enough cpu to
:     run a TCP stack at that speed :-)

Aye, there's the rub - is there enough CPU.

:     A pentium pro 200 with parity non-edo ram has about 200 MBytes/sec of 
:     dynamic ram throughput.  The PCI bus has 133 MBytes/sec of throughput
:     (and I've actually run PCI DMA at 115 MBytes/sec, so I know it can
:     do it!).  No problem !  :-) :-)

:)

:     The real question is what is the Interrupt/TCP/IP stack overhead for
:     FreeBSD on a pentium-pro 200?

Well, fire-up a netperf test with 10 or 100BaseT, I doubt it really
matters so long as they both have decent drivers (DMA, not PIO) and
measure the CPU usage. If the machine takes more than 1% CPU
to do 10 BaseT or 10% to do 100 BT, it won't do link-rate 1000BT ;)

rick jones