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    SubjectRe: PERF: performance tests with the split LRU VM in -mm
    On Mon, Jul 28, 2008 at 7:57 AM, Rik van Riel <> wrote:
    > 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.

    Or the IOs are getting sent in a different order, and so
    coalescing/merging isn't occurring as often. Getting some
    instrumentation (something as simple as a histogram) on the IO sizes
    could be useful.

     \ /
      Last update: 2008-07-28 17:33    [W:0.097 / U:3.528 seconds]
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