Date: Wed, 18 Jun 1997 23:11:54 +0200 From: sthaug@nethelp.no To: tom@sdf.com Cc: ccsanady@scl.ameslab.gov, hackers@FreeBSD.ORG, matt@3am-software.com Subject: Re: Network concurrency problems!? Message-ID: <4913.866668314@verdi.nethelp.no> In-Reply-To: Your message of "Wed, 18 Jun 1997 13:48:01 -0700 (PDT)" References: <Pine.BSF.3.95q.970618134115.11180D-100000@misery.sdf.com>
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> > Also, if you expect a PPro-200 to saturate 4 100 Mbps links, I think you > > are a wee bit optimistic. (One link, no problem.) > > Why? As long as the ethernet hw is fast, is should be no problem. It's a problem because of the resource usage of the TCP/IP stack and the driver. The FreeBSD TCP/IP stack is good, but it's not the most efficient. As far as I know, there is still an extra pass over the data to perform the TCP checksum, for instance. > I > can run 2 FW SCSI channels saturated (2 x 20MB/s * 8 = 320mbs), and the > system isn't even working too hard yet. Certainly, full-duplex > connections double the total possible bandwidth (4 x 100 x 2 = 800mbs), > but most servers are mainly outbound. > > However, I really doubt whether most ethernet adapters offload enough > functions from the main CPU. The trend is to make very stupid > controllers, which are slaved to the CPU for everything. There has been a good deal of debate on whether offloading is really the best idea for network protocol implementations. A lot of people have tried it, and a lot of people have failed. If you look at Van Jacobson't work you'll find him arguing in the opposite direction: A "stupid" (in reality: simple and efficient) controller, and a very efficient protocol stack implementation. See http://ee.lbl.gov/nrg-talks.html, in particular "Some Design Issues for High-speed Networks" and "Design Changes to the Kernel Network Architecture for 4.4BSD" Also "The Witless Interface", presented at the 1991 Gigabit Workshop. Steinar Haug, Nethelp consulting, sthaug@nethelp.no
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