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    SubjectRe: [RFC][PATCH 0/6] perf: x86 RDPMC and RDTSC support
    On 11/21/2011 10:02 AM, Vince Weaver wrote:
    > On Mon, 21 Nov 2011, Peter Zijlstra wrote:
    >
    >> These few patches implement x86 RDPMC support and add an extention to the self
    >> monitoring data to also allow additional time updates using userspace TSC reads.
    >>
    >> There's a few loose ends, but it mostly seems to work.
    >
    > I'll have to test these out.
    >
    > I have some low-level benchmarks I've been working on, you can see some
    > preliminary results here:
    > http://web.eecs.utk.edu/~vweaver1/projects/perf-events/benchmarks/
    >
    > perf_events was lagging behind perfmon2 and perfctr in self-monitoring
    > overhead, but maybe these changes will help that.
    >
    > perf_event overhead got a lot worse between 2.6.32 and 3.0, I'm mid-bisect
    > on that trying to isolate the cause.
    >
    > Vince
    >

    Hi Vince,

    Any improvements in performance of self-monitoring would be welcomed. International Symposium on computer Architecture (ISCA 2011) has paper about a low overhead mechanism to read out the performance counters, LiMiT (http://castl.cs.columbia.edu/limit/index.php/LiMiT) that avoids using system calls to read the performance counter data. That paper shows a fair amount of overhead for PAPI.

    -Will


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