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    SubjectRe: OSDI paper - IO-Lite: A Unified I/O Buffering and Caching System


    > From: Oliver Xymoron <oxymoron@waste.org>
    > Date: Tue, 2 Mar 1999 23:41:28 -0600 (CST)
    > To: Jim Gettys <jg@pa.dec.com>
    > Cc: linux-kernel <linux-kernel@vger.rutgers.edu>
    > Subject: Re: OSDI paper - IO-Lite: A Unified I/O Buffering and Caching System
    > -----
    > On Tue, 2 Mar 1999, Jim Gettys wrote:
    >
    > > It shows a new I/O approach that is very general and flexible, and avoids
    > > data copies with minimal overhead, even between processes. The authors
    > > use as an example Web service, and show very good performance gains.
    >
    > Very interesting. We probably wouldn't see quite the gains the author saw
    > with his FreeBSD implementation. It's a good match for FreeBSD as it
    > already has a zero-copy scheme in a lot of areas and fits better with
    > their design philosophy. Linux largely avoids VM manipulations like those
    > suggested for instance by I/O-Lite's IPC scheme, because of their nasty
    > effect on CPU caches, SMP scaling, etc. So parts of it are going to be a
    > hard sell. And we've got sendfile(2) now, which is not nearly as pretty or
    > generic, but might still give similar performance at least for the common
    > web server case.
    >
    >

    Sendfile does not help the CGI case, which is very common (or dominant)
    on many (most) high volume servers.

    I believe it will also help the CPU cache case for CGI; it avoids having
    to touch the data again in many operations, which would pollute the cache
    with data that was merely copied in the web server.
    - Jim



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