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    SubjectRe: [Ext2-devel] disk throughput
    On Sun, Nov 04 2001, Mike Fedyk wrote:
    > On Mon, Nov 05, 2001 at 08:06:35AM +0100, Jens Axboe wrote:
    > > On Sun, Nov 04 2001, Andrew Morton wrote:
    > > > The meaning of the parameter to elvtune is a complete mystery, and the
    > > > code is uncommented crud (tautology). So I just used -r20000 -w20000.
    > >
    > > It's the number of sectors that are allowed to pass a request on the
    > > queue, because of merges or inserts before that particular request. So
    > > you want lower than that probably, and you want READ latency to be
    > > smaller than WRITE latency too. The default I set is 8192/16384 iirc, so
    > > go lower than this -- -r512 -w1024 or even lower just to check the
    > > results.
    > >
    >
    > Does the elevator do better with powers of two?

    No, that doesn't matter.

    > > > This was based on observing the request queue dynamics. We frequently
    > > > fail to merge requests which really should be merged regardless of
    > > > latency. Bumping the elvtune settings fixed it all. But once the
    > > > fs starts writing data out contiguously it's all academic.
    > >
    > > Interesting, the 2.5 design prevents this since it doesn't account
    > > merges as a penalty (like a seek). I can do something like that for 2.4
    > > too, I'll do a patch for you to test.
    > >
    >
    > I'd be very interested in this patch. Can you post it pubically?

    Just posted :-)

    --
    Jens Axboe

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