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    SubjectRe: [Ext2-devel] disk throughput
    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?

    > > 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?

    > --
    > Jens Axboe
    >

    Mike
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