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Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!munnari.OZ.AU!news.ecn.uoknor.edu!solace!nntp.uio.no!nntp.uib.no!nntp-bergen.UNINETT.no!nntp-trd.UNINETT.no!not-for-mail From: sthaug@nethelp.no (Steinar Haug) Newsgroups: comp.os.linux.networking,comp.unix.bsd.netbsd.misc,comp.unix.freebsd.misc Subject: Re: TCP latency Date: 02 Jul 1996 22:42:08 GMT Organization: Nethelp Consulting, Trondheim, Norway Lines: 48 Message-ID: <4rc8k0$ec0@verdi.nethelp.no> References: <4paedl$4bm@engnews2.Eng.Sun.COM> <4pf7f9$bsf@white.twinsun.com> <4qad7d$a5l@verdi.nethelp.no> <4qaui4$o5k@fido.asd.sgi.com> <4qc60n$d8m@verdi.nethelp.no> <31D2F0C6.167EB0E7@inuxs.att.com> NNTP-Posting-Host: trane.uninett.no In-reply-to: "John S. Dyson"'s message of Thu, 27 Jun 1996 15:36:22 -0500 Xref: euryale.cc.adfa.oz.au comp.os.linux.networking:43781 comp.unix.bsd.netbsd.misc:3910 ["John S. Dyson"] | > Pentium local 250 usec | > AMD Linux local 330 usec | > AMD FreeBSD local 350 usec | > AMD Linux -> Pentium 420 usec | > AMD FreeBSD -> Pentium 520 usec | > | > So the difference is quite noticeable. Wish I had another P133 here to | > test with, but unfortunately I don't. | > | All this TCP latency discussion is interesting, but how does this | significantly impact performance when streaming data through the | connection? Isn't TCP a streaming protocol? Yes, *but* a lot of people also use it for (small) transactions, where latency is important. | Was TTCP used in these | tests? I would think that if you were doing that many connections per | second, TTCP would be better generally (like for WWW servers.) Of course TTCP would be better, but it's not as readily available, and therefore standard TCP latency *is* of interest. Yes, I know TTCP is available in FreeBSD. | Isn't this just a connection latency? Hmmm... Data | througput starts overshadowing connection latency quickly. Also, | there is some latency that does not really imply CPU usage... The measurements give you some idea of the *minimum* latency. This is relevant for small, short transactions. With 10 Mbit/s Ethernet, you can have something like 64 byte of data for a request and 512 byte of data for the answer before the time to move the data on the wire starts approaching the 520 usec figure above. With 100 Mbit/s Ethernet, much more data, of course. (But with 100 Mbit/s Ethernet the figures above are smaller in the first place.) | Interesting data point, but really doesn't appear to impact system | performance much if at all. | | Isn't meaningless benchmarking fun!!! Again, it all depends on what you use your system for. I certainly agree that this is only one small factor of the total system performance. For some people this part is important, for others less so. Steinar Haug, Nethelp consulting, sthaug@nethelp.no