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    SubjectRe: PERF: performance tests with the split LRU VM in -mm
    On Thu, 24 Jul 2008 22:25:10 -0400
    Rik van Riel <> wrote:

    > TEST 1: dd if=/dev/sda of=/dev/null bs=1M
    > kernel speed swap used
    > 2.6.26 111MB/s 500kB
    > -mm 110MB/s 59MB (ouch, system noticably slower)
    > noforce 111MB/s 128kB
    > stream 108MB/s 0 (slight regression, not sure why yet)
    > This patch shows that the split LRU VM in -mm has a problem
    > with large streaming IOs: the working set gets pushed out of
    > memory, which makes doing anything else during the big streaming
    > IO kind of painful.
    > However, either of the two patches posted fixes that problem,
    > though at a slight performance penalty for the "stream" patch.

    OK, the throughput number with this test turns out not to mean
    nearly as much as I thought.

    Switching off CPU frequency scaling, pinning the CPUs at the
    highest speed, resulted in a throughput of only 102MB/s.

    My suspicion is that faster running code on the CPU results
    in IOs being sent down to the device faster, resulting in
    smaller IOs and lower throughput.

    This would be promising for the "stream" patch, which makes
    choosing between the two patches harder :)

    Andrew, what is your preference between:

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      Last update: 2008-07-28 17:01    [W:0.020 / U:107.028 seconds]
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