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    SubjectRe: [PATCH 2/2] perf_counter: optimize context switch between identical inherited contexts
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    On Fri, 2009-05-22 at 11:22 +0200, Peter Zijlstra wrote:
    > On Fri, 2009-05-22 at 14:27 +1000, Paul Mackerras wrote:
    > >
    > > -----Unmodified----- With this patch series
    > > Counters: none 2 HW 4H+4S none 2 HW 4H+4S
    > >
    > > 2 processes:
    > > Average 3.44 6.45 11.24 3.12 3.39 3.60
    > > St dev 0.04 0.04 0.13 0.05 0.17 0.19
    > >
    > > 8 processes:
    > > Average 6.45 8.79 14.00 5.57 6.23 7.57
    > > St dev 1.27 1.04 0.88 1.42 1.46 1.42
    > >
    > > 32 processes:
    > > Average 5.56 8.43 13.78 5.28 5.55 7.15
    > > St dev 0.41 0.47 0.53 0.54 0.57 0.81
    >
    > Any clues as to why the time is still dependent on the number of
    > counters in the context? The approach seems to be O(1) in that it
    > does a simple counter context swap on sched_out and nothing on sched_in.

    Ah, should I read this as 'n' lmbench instances on a single cpu? So that
    we get multiple inheritance sets mixed and have to switch between them?



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