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    SubjectRe: [PATCH v2 1/2] perf tools: Add support for pinned modifier
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    Hi Michael,

    On Tue, 6 Aug 2013 23:28:05 +1000, Michael Ellerman wrote:
    > This commit adds support for a new modifier "D", which requests that the
    > event, or group of events, be pinned to the PMU.
    >
    > The "p" modifier is already taken for precise, and "P" may be used in
    > future to mean "fully precise".
    >
    > So we use "D", which stands for pinneD - and looks like a padlock, or if
    > you're using the ":D" syntax perf smiles at you.
    >
    > This is an oft-requested feature from our HW folks, who want to be able
    > to run a large number of events, but also want 100% accurate results for
    > instructions per cycle.
    >
    > Comparison of results with and without pinning:
    >
    > $ perf stat -e '{cycles,instructions}:D' -e cycles,instructions,...
    >
    > 79,590,480,683 cycles # 0.000 GHz
    > 166,123,716,524 instructions # 2.09 insns per cycle
    > # 0.11 stalled cycles per insn
    >
    > 79,352,134,463 cycles # 0.000 GHz [11.11%]
    > 165,178,301,818 instructions # 2.08 insns per cycle
    > # 0.11 stalled cycles per insn [11.13%]
    >
    > As you can see although perf does a very good job of scaling the values
    > in the non-pinned case, there is some small discrepancy.
    >
    > The patch is fairly straight forward, the one detail is that we need to
    > make sure we only request pinning for the group leader when we have a
    > group.

    Acked-by: Namhyung Kim <namhyung@kernel.org>

    Thanks,
    Namhyung


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