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    SubjectRe: [PATCH 1/2] perf-events: Add support for supplementary event registers v2
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    On Fri, 2010-11-12 at 18:17 +0100, Stephane Eranian wrote:
    > I looked at this patch thinking how could this be reused for LBR_SELECT.
    >
    > I am wondering if storing the extra MSR value in attr.config is really the way
    > to go now as opposed to adding/overloading a field.
    >
    > For OFFCORE_RESPONSE, it makes sense to use attr.config because this is
    > a refinement of the event (a sub-sub event if you want).

    Correct, it makes sense for offcore and load-latency, not so much for
    lbr_config.

    > For LBR_SELECT, you also need to pass a value, but there is no specific event
    > associated with it. You can enable LBR with any event you want. Thus,
    > storing the
    > LBR_SELECT value independently would also make sense. And if we have this
    > field for LBR_SELECT then we may as well use it for OFFCORE_REPONSE.

    That would assume a single event doesn't contain offcore and lbr, no?
    Currently the extra_reg thing assumes there's only one extra reg encoded
    in the config word.

    > The alternative would be to consider LBR_SELECT also as a refinement of
    > the event being measured. Though by itself, it wouldn't do anything, it would
    > have to be combine with a PERF_SAMPLE_BRANCH_STACK to attr.sample_type.

    A separate field for the lbr_config seems to make most sense, we could
    of course use the top 16 bits for lbr, the next 16 for offcore/ll and
    the bottom 32 for eventsel, but that's mighty crowded.




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