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    SubjectRe: [PATCH 2/3] perf: Add support for extra parameters for raw events
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    On Fri, 2010-11-12 at 14:00 +0100, Stephane Eranian wrote:
    > I don't understand what aspect you think is messy. When you are sampling
    > cache misses, you expect to get the tuple (instr addr, data addr, latency,
    > data source).

    Its the data source thing I have most trouble with -- see below. The
    latency isn't immediately clear either, I mean the larger the bubble the
    more hits the instruction will get, so there should be a correlation
    between samples and latency.

    > That is what you get with AMD IBS, Nehalem PEBS-LL and
    > also Itanium D-EAR. I am sure IBM Power has something similar as well.
    > To collect this, you can either store the info in registers (AMD, Itanium)
    > or in a buffer (PEBS). But regardless of that you will always have to expose
    > the tuple. We have a solution for two out of 4 fields that reuses the existing
    > infrastructure. We need something else for the other two.

    Well, if Intel PEBS, IA64 and PPC64 all have a data source thing we can
    simply add PERF_SAMPLE_SOURCE or somesuch and use that.

    Do IA64/PPC64 have latency fields as well? PERF_SAMPLE_LATENCY would
    seem to be the thing to use in that case.

    BTW, what's the status of perf on IA64? And do we really still care
    about that platform, its pretty much dead isn't it?

    > We should expect that in the future PMUs will collect more than code addresses.

    Sure, but I hate stuff that counts multiple events on a single base like
    IBS does, and LL is similar to that, its a fetch retire counter and then
    you report where fetch was satisfied from. So in effect you're measuring
    l1/l2/l3/dram hit/miss all at the same time but on a fetch basis.

    Note that we need proper userspace for such crap as well, and libpfm
    doesn't count, we need a full analysis tool in perf itself.


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