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    SubjectRe: [PATCH] Avoid preferential treatment of groups that aren't backlogged
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    On Wed, Feb 9, 2011 at 6:09 PM, Vivek Goyal <vgoyal@redhat.com> wrote:
    > In upstream code once a group gets backlogged we put it at the end
    > and not at the beginning of the tree. (I am wondering are you looking
    > at the google internal code :-))
    >
    > So I don't think that issue of a low weight group getting more disk
    > time than its fair share is present in upstream kernels.

    You've caught me re-using a commit description. :)

    Here's an example of the kind of tests that fail without this patch
    (run via the test that Justin and Akshay have posted):

    15:35:35 INFO ----- Running experiment 14: 950 rdrand, 50 rdrand.delay10
    15:35:55 INFO Experiment completed in 20.4 seconds
    15:35:55 INFO experiment 14 achieved DTFs: 886, 113
    15:35:55 INFO experiment 14 FAILED: max observed error is 64, allowed is 50

    15:35:55 INFO ----- Running experiment 15: 950 rdrand, 50 rdrand.delay50
    15:36:16 INFO Experiment completed in 20.5 seconds
    15:36:16 INFO experiment 15 achieved DTFs: 891, 108
    15:36:16 INFO experiment 15 FAILED: max observed error is 59, allowed is 50

    Since this is Jens' unmodified tree, I've had to change
    BLKIO_WEIGHT_MIN to 10 to allow this test to proceed. We typically
    run many jobs with small weights, and achieve the requested isolation:
    see below results with this patch:

    14:59:17 INFO ----- Running experiment 14: 950 rdrand, 50 rdrand.delay10
    14:59:36 INFO Experiment completed in 19.0 seconds
    14:59:36 INFO experiment 14 achieved DTFs: 947, 52
    14:59:36 INFO experiment 14 PASSED: max observed error is 3, allowed is 50

    14:59:36 INFO ----- Running experiment 15: 950 rdrand, 50 rdrand.delay50
    14:59:55 INFO Experiment completed in 18.5 seconds
    14:59:55 INFO experiment 15 achieved DTFs: 944, 55
    14:59:55 INFO experiment 15 PASSED: max observed error is 6, allowed is 50

    As you can see, it's with seeky workloads that come and go from the
    service tree where this patch is required.

    Chad


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