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    SubjectRe: [PATCHv3 0/3] perf tool: Add new event group management
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    On Mon, Jul 2, 2012 at 3:33 PM, Jiri Olsa <jolsa@redhat.com> wrote:
    > On Mon, Jul 02, 2012 at 10:11:02PM +0900, Namhyung Kim wrote:
    >> 2012-07-02 (월), 12:15 +0200, Jiri Olsa:
    >> > On Mon, Jul 02, 2012 at 10:53:44AM +0900, Namhyung Kim wrote:
    >> > > Just a question, is there a way to know about the grouping at perf
    >> > > report time?
    >> >
    >> > nope, AFAIK only ID and perf_event_attr is stored for event
    >> > grouping is known only for record time
    >> >
    >>
    >> I heard that Arnaldo (or Stephane) wanted to make perf report
    >> group-aware or such so that it can show related events together. But to
    >> do that, it seems we need to change the data file format first, right?
    >>
    >> Any idea?
    >
    > The next change I'm working on is to record and report
    > PERF_FORMAT_GROUP related data. Here's commit comment
    > from my next patchset:
    >
    > ---
    > perf, tool: Enable sampling on specified event group leader
    >
    > Adding the functionality to the group modifier event syntax.
    > Allowing user to select leader event inside the group using
    > event index (command line event position in the group).
    >
    > Following example selects e2 as leader:
    > -e '{e1,e2,e3,e4}:2'
    >
    I don't understand why you actually need the :2 suffix. There can
    only be one leader. So assume it is the first one. Users have to
    know the first one is the leader which seems like a natural thing
    to do for me. It would make you syntax less ugly than it already
    is.

    I would have thought you could enable this with a simple
    cmdline option which changes the way you interpret the
    multiple -e options:

    perf record --group-reads -e e1,e2,e3 -e e4,e5,e6 .....

    Would setup the group leaders (e1, e4) for 2 groups.
    NO curly braces, no : needed.

    > The selected event becomes group leader and is the only one
    > doing samples.
    >
    > The rest of the events in the group are being read on each leader
    > event sample by PERF_SAMPLE_READ sample type processing.
    >
    > Following example:
    > perf record -e {cycles,faults}:1 ls
    >
    > - creates a group with 'cycles' and 'faults' events
    > - 'cycles' event is group leader and has sampling enabled
    > - 'faults' event is read each time 'cycles' sample,
    > the 'faults' count is attached to the 'cycles sample
    > via PERF_SAMPLE_READ sample type.
    > ---
    >
    > The report does not need any new metadata about grouping, because
    > the samples are generated/stored only from the group leader. The
    > other events data are read from the PERF_FORMAT_GROUP leader sample
    > data.
    >
    > So no data file format change for my next changes, but I'm not sure
    > this is the report change you mean.
    >
    > jirka
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