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    SubjectRe: [PATCH 0/9] cgroup: io-throttle controller (v13)
    On Thu, Apr 30, 2009 at 09:20:58AM -0400, Alan D. Brunelle wrote:
    > Hi Andrea -

    Hi Alan,

    >
    > FYI: I ran a simple test using this code to try and gauge the overhead
    > incurred by enabling this technology. Using a single 400GB volume split
    > into two 200GB partitions I ran two processes in parallel performing a
    > mkfs (ext2) on each partition. First w/out cgroup io-throttle and then
    > with it enabled (with each task having throttling enabled to
    > 400MB/second (much, much more than the device is actually capable of
    > doing)). The idea here is to see the base overhead of just having the
    > io-throttle code in the paths.

    Interesting. I've never explicitly measured the actual overhead of the
    io-throttle infrastructure, I'll add a similar test to the io-throttle
    testcase.

    >
    > Doing 30 runs of each (w/out & w/ io-throttle enabled) shows very little
    > difference (time in seconds)
    >
    > w/out: min=80.196 avg=80.585 max=81.030 sdev=0.215 spread=0.834
    > with: min=80.402 avg=80.836 max=81.623 sdev=0.327 spread=1.221
    >
    > So only around 0.3% overhead - and that may not be conclusive with the
    > standard deviations seen.

    You should see less overhead with reads respect to a pure write
    workload, because with reads we don't need to check if the IO request
    occurs in a different IO context. And things should be improved with
    v16-rc1
    (http://download.systemimager.org/~arighi/linux/patches/io-throttle/cgroup-io-throttle-v16-rc1.patch).

    So, it would be also interesting to analyse the overhead of a read
    stream compared to a write stream, as well a comparison of random
    reads/writes. I'll do that in my next benchmarking session.

    >
    > --
    >
    > FYI: The test was run on 2.6.30-rc1+your patches on a 16-way x86_64 box
    > (128GB RAM) plus a single FC volume off of a 1Gb FC RAID controller.
    >
    > Regards,
    > Alan D. Brunelle
    > Hewlett-Packard

    Thanks for posting these results,
    -Andrea


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