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    SubjectRe: Odd IDE performance drop 2.4 vs 2.6?
    Alan Cox wrote:
    > On Llu, 2005-06-13 at 15:06, Nick Piggin wrote:
    >
    >>>Make sure you have pre-empt disabled and the antcipatory I/O scheduler
    >>>disabled.
    >>>
    >>
    >>I don't think that those could explain it.
    >
    >
    > Try it and see. The anticipatory I/O scheduler does horrible things to
    > my IDE streaming performance numbers and to swap performance. It tries
    > to merge I/O by delaying it which is deeply ungood when it comes to IDE
    > streaming even if its good for general I/O.

    Changing the scheduler did not help (the results are about the same with
    any of the 4 schedulers). Read ahead is already set to 256 (increasing
    to 1024 did not help either). Kernel compilation takes too much time
    here so I didn't test with preempt disabled.
    The drive is WD300BB (7200RPM) in UDMA2 mode.

    root@pentium:~# cat /sys/block/hda/queue/scheduler
    noop anticipatory [deadline] cfq
    root@pentium:~# hdparm -tT /dev/hda

    /dev/hda:
    Timing cached reads: 176 MB in 2.00 seconds = 88.00 MB/sec
    Timing buffered disk reads: 34 MB in 3.02 seconds = 11.26 MB/sec
    root@pentium:~# hdparm /dev/hda

    /dev/hda:
    multcount = 16 (on)
    IO_support = 1 (32-bit)
    unmaskirq = 1 (on)
    using_dma = 1 (on)
    keepsettings = 1 (on)
    readonly = 0 (off)
    readahead = 256 (on)
    geometry = 58168/16/63, sectors = 58633344, start = 0


    --
    Ondrej Zary
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