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    SubjectRe: [PATCH V7 07/14] perf/core: Add a new PERF_EV_CAP_COEXIST event capability
    On Fri, Jul 24, 2020 at 04:59:34PM +0200, Peter Zijlstra wrote:
    > On Fri, Jul 24, 2020 at 07:46:32AM -0700, Andi Kleen wrote:
    > > > Something that seems to 'work' is:
    > > > '{cycles,cpu/instructions,period=50000/}', so maybe you can make the
    > > > group modifier :S use any sampling event if there is one, and otherwise
    > > > designate the leader.
    > > >
    > > > Then you can write things like:
    > > >
    > > > '{slots, metric1, metric2, cpu/cycles,freq=50000/}:S'
    > > >
    > > > and then since cycles is specified as a sampling event, it will use
    > > > that.
    > >
    > > Okay possible, but it makes things more complicated
    > > for the user to understand and requires special documentation.
    > > Hopefully it's worth it the internal simplification.
    >
    > You already require special documentation for this metrics stuff. We
    > already need to state that SLOTS cannot be a sampling event, so you
    > already need to pay attention to this anyway.
    >
    > A shortcut could be a :s event modifier, then you can write:
    >
    > '{slots, metric1, metric2, cycles:s}:S'
    >
    > and have the tool select the :s tagged one.

    Having slots as leader also would allow doing something like
    FORMAT_METRIC, where we return sibling/leader in some fashion.

    That also makes sense for instructions, because, IIRC,
    instructions/slots is the better IPC.

    And we should probably consider FORMAT_RESET.

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