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    SubjectRe: [PATCH 2/3] x86: Implement prctl PR_GET_TSC and PR_SET_TSC


    On Sat, 12 Apr 2008, H. Peter Anvin wrote:

    >
    > I also saw no mention about performance impact, which need to be
    > considered whenever *anything* is proposed to be inserted into a hot
    > path. It may be (heck, *should be*) that the performance impact isn't
    > measurable, but that needs to be positively established.
    >
    > -hpa
    >

    It took me a while, but I have done some tests om my system with and
    without my patch applied.

    All deamons but klogd/syslogd were shut down andI used the following
    command:

    LMBENCH_SCHED="SINGLE" \
    /usr/lib/lmbench/bin/{i686-pc,x86_64}-linux-gnu/lat_ctx -s 0 2

    The variation was quite high so I ran it a 1000 times for each
    configuration.

    x86_32, patch applied, 1000x repeated, avg: 1.319, rmse: 0.081
    x86_32, patch not applied, 1000x repeated, avg: 1.335, rmse: 0.107

    x86_64, patch applied, 1000x repeated, avg: 1.417, rmse: 0.0716
    x86_64, patch not applied, 1000x repeated, avg: 1.423, rmse: 0.0745

    This is on a core 2 duo E6300.

    Erik


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