*BSD News Article 74096


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From: iialan@iifeak.swan.ac.uk (Alan Cox)
Newsgroups: comp.os.linux.networking,comp.unix.bsd.netbsd.misc,comp.unix.bsd.freebsd.misc
Subject: Re: TCP latency
Date: 18 Jul 1996 10:07:00 GMT
Organization: Institute For Industrial Information Technology
Lines: 19
Message-ID: <4sl2c4$jf5@news.swan.ac.uk>
References: <4sbhrq$msh@enomem.lkg.dec.com> <31E995B6.573A3461@lambert.org> <4schqh$ssa@panix2.panix.com>
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Xref: euryale.cc.adfa.oz.au comp.os.linux.networking:45653 comp.unix.bsd.netbsd.misc:4106 comp.unix.bsd.freebsd.misc:23902

In article <4schqh$ssa@panix2.panix.com> tls@panix.com (Thor Lancelot Simon) writes:
>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...

On the PC its quite painful since you don't have a handy  "invalidate one
TLB" type instruction. On a multiprocessor box it can get more involved as
well. If you can find an mmap() semantic then it is a win because you also
remove the cost of the TLB and page table change hits as the page is already
mapped and stays mapped shared with the socket. The problem is much more
what does mmap on a socket mean

Alan
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