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    SubjectRe: [RFC PATCHv3] perf tools: add event grouping capability to "perf stat"
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    On Thu, 2010-11-25 at 14:19 +0100, Stephane Eranian wrote:

    > I think using PERF_SAMPLE_READ may expose a problem in the
    > perf.data format. To correctly parse a sample created with SAMPLE_READ,
    > you need to know the attr.read_format. But for that you need to know the
    > event which caused the sample, but for that you need the SAMPLE_ID,
    > and you don't know if it's there or not. In other words, there is a chicken
    > and egg problem.
    >
    > I think the issue is that PERF_RECORD_SAMPLE is missing a mandatory
    > piece of information: overflow event ID. This must a mandatory field, not
    > optional as it is today. It is okay when you have only one group, but we'd
    > like to go beyond that.



    I'm not sure I get it, there's both PERF_FORMAT_ID and PERF_SAMPLE_ID,
    so afaict there's a working combination for what you want to do.




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