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    SubjectRe: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest]
    On Mon, Feb 10, 2003 at 01:07:25PM +0300, Hans Reiser wrote:
    > Andrew Morton wrote:
    > >
    > >Large directories tend to be spread all around the disk anyway. And I've
    > >never explicitly tested for any problems which the loss of readahead might
    > >have caused ext2. Nor have I tested inode table readahead. Guess I
    > >should.
    > >
    > >
    > >-
    > >To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    > >the body of a message to
    > >More majordomo info at
    > >Please read the FAQ at
    > >
    > >
    > >
    > >
    > readahead seems to be less effective for non-sequential objects. Or at

    yes, this is why I said readahead matters mostly to generate the big dma
    commands, so if the object is sequential it will be served by the
    lowlevel with a single dma using SG. this is also why when I moved the
    high dma limit of scsi to 512k (from 128k IIRC) I got such a relevant
    throughput improvement. Also watch the read speed in my tree compared to
    2.4 and 2.5 in bigbox.html from Randy (bonnie shows it well).

    > least, you don't get the order of magnitude benefit from doing only one
    > seek, you only get the better elevator scheduling from having more
    > things in the elevator, which isn't such a big gain.


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