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    SubjectRe: IO scheduler benchmarking
    David Lang <david.lang@digitalinsight.com> wrote:
    >
    > one other useful test would be the time to copy a large (multi-gig) file.
    > currently this takes forever and uses very little fo the disk bandwidth, I
    > suspect that the AS would give more preference to reads and therefor would
    > go faster.

    Yes, that's a test.

    time (cp 1-gig-file foo ; sync)

    2.5.62-mm2,AS: 1:22.36
    2.5.62-mm2,CFQ: 1:25.54
    2.5.62-mm2,deadline: 1:11.03
    2.4.21-pre4: 1:07.69

    Well gee.


    > for a real-world example, mozilla downloads files to a temp directory and
    > then copies it to the premanent location. When I download a video from my
    > tivo it takes ~20 min to download a 1G video, during which time the system
    > is perfectly responsive, then after the download completes when mozilla
    > copies it to the real destination (on a seperate disk so it is a copy, not
    > just a move) the system becomes completely unresponsive to anything
    > requireing disk IO for several min.

    Well 2.4 is unreponsive period. That's due to problems in the VM - processes
    which are trying to allocate memory get continually DoS'ed by `cp' in page
    reclaim.

    For the reads-starved-by-writes problem which you describe, you'll see that
    quite a few of the tests did cover that. contest does as well.

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