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From: tls@panix.com (Thor Lancelot Simon)
Newsgroups: comp.os.linux.networking,comp.unix.bsd.netbsd.misc,comp.unix.bsd.freebsd.misc
Subject: TCP latency
Supersedes: <4schf6$sbl@panix2.panix.com>
Date: 15 Jul 1996 00:35:29 -0400
Organization: Panix
Lines: 34
Message-ID: <4schqh$ssa@panix2.panix.com>
References: <4paedl$4bm@engnews2.eng.sun.com> <m24tnf9f69.fsf@frob.mlm.extern.lrz-muenchen.de> <4sbhrq$msh@enomem.lkg.dec.com> <31E995B6.573A3461@lambert.org>
NNTP-Posting-Host: panix2.panix.com
Xref: euryale.cc.adfa.oz.au comp.os.linux.networking:45222 comp.unix.bsd.netbsd.misc:4046 comp.unix.bsd.freebsd.misc:23581
In article <31E995B6.573A3461@lambert.org>,
Terry Lambert <terry@lambert.org> wrote:
>Matt Thomas wrote:
>] In article <m24tnf9f69.fsf@frob.mlm.extern.lrz-muenchen.de>,
>] Andi Kleen <andi@mlm.extern.lrz-muenchen.de> writes:
>]
>] >I think a mmap() interface to sockets would be more elegant (and
>] >you could do exactly the same thing)
>]
>] I can't see how mmap() would map to a socket. Unlike a file,
>] you can't directly address portions of a communication stream.
>] What would lseek do? Sockets have semantics that are very
>] sequential in nature. mmap is not a good fit.
>]
>] How would you use mmap on a pipe?
>
>You would map the buffer into both the source and target
>applications address spaces, and avoid the user->kernel->user
>copies.
If you want to do that, don't you want to just change copyin/copyout to
copy any unaligned portion at either end, and then map instead of copying
the middle? This wins for everything, without requiring a change in
user-level semantics.
I was lucky enough to get to discuss this with Kirk McKusick at one point
a few months ago. He indicated that at least one version of Mach had done
exactly that on the VAX, and that it turned out to be a win iff you wanted
to move more than about 8K. Of course, that number is so utterly hardware
dependent...
--
Thor Lancelot Simon tls@panix.COM
"Gee, if your knee jerks any harder you're going to kick yourself in the head."
-- Barry Sherman