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    SubjectRe: O_DIRECT performance impact on 2.4.18 (was: Re: [PATCH] 2.5.14 IDE 56)
    On Sat, May 11 2002, Roy Sigurd Karlsbakk wrote:
    > On Friday 10 May 2002 17:55, Linus Torvalds wrote:
    > > On Fri, 10 May 2002, Lincoln Dale wrote:
    > > > so O_DIRECT in 2.4.18 still shows up as a 55% performance hit versus no
    > > > O_DIRECT. anyone have any clues?
    > >
    > > Yes.
    > >
    > > O_DIRECT isn't doing any read-ahead.
    > >
    > > For O_DIRECT to be a win, you need to make it asynchronous.
    >
    > Will the use of O_DIRECT affect disk elevatoring?

    No, the I/O scheduler can't even tell whether it's being handed
    O_DIRECT buffers or not.

    Jens
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