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From: Pedro Roque Marques <roque@di.fc.ul.pt>
Newsgroups: comp.os.linux.networking,comp.unix.bsd.netbsd.misc,comp.unix.bsd.freebsd.misc
Subject: Re: TCP latency
Date: 08 Jul 1996 22:05:38 +0100
Organization: Faculdade de Ciencias da Universidade de Lisboa
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>>>>> "tedm" == tedm <tedm@agora.rdrop.com> writes:
tedm> I feel this has gotten so academic that it is meaningless.
I for one i'm so tired of seing non-techical arguments on Usenet about
supposedly techincal issues that i don't ever consider a discussion to
get "too academic".
tedm> Who cares what the latency/throughput figures are or who is
tedm> winning the current benchmark in vogue!
There is two things here:
I for one care about the latency/thoughtput figures since it helps to
evaluate the code i intend to test and work on. I really don't care
about who is winning but that is not to say that a comparison, when
numbers are largely different is not useful.
tedm> The fact is that these numbers only become important on
tedm> servers that are being used to serve users, which strikes
tedm> out 90% of the personal Unix boxes out there in my opinion.
Having good thoughput and/or latency in TCP is much harder than most
people believe. There is a full load of things going on in a TCP stack
that are very dificult to deal with. If you want an precise example
the BSD stack evolution from 4.2 to 4.4 has greatly improved those
figures, the more important work on this, done over *years*, was done
by the LBL people and specially Van Jacobson. Curiously enhough if you
read his mails from the time you find several references to both
thoughput and latency messured with unloaded machines.
For someone that is working on the subject this numbers are very
important. Believe me, i've been playing recently with stuff like when
preciselly to send an ack and such and those figures really show when
i screw up (which is more frequent that what i would like to admit).
When to send an ack is not at all trivial by the TCP specs and
influences bandwidth utilization and shows up on the latency test (if
you send extra acks) or completly breaks your interactive performance
(if you send too little or too delayed acks).
Now, can we have technical discussions between people regardless of
their religious belief or choice of operating system ? There is a lot
of stuff that i would like to learn with the BSD people... by acident
i might even be hable to contribute something back to the pool.
regards,
Pedro.