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    SubjectRe: [PATCH] perf tools: Exit recording if events have non matching sample type


    On 09/29/2011 06:40 PM, Arnaldo Carvalho de Melo wrote:
    > Em Thu, Sep 29, 2011 at 05:33:42PM -0600, David Ahern escreveu:
    >> On 09/29/2011 05:06 PM, Arnaldo Carvalho de Melo wrote:
    >>>> >From what I can see sample_type has to be the same for all samples:
    >>>> https://lkml.org/lkml/2011/8/15/6
    >
    >>> We could add a PERF_SAMPLE_ID2 that if present would be guaranteed
    >>> to be the last, or we can, as PeterZ prefers/suggests, to use one
    >>> mmap per sample id, then we know that if we're getting it on that
    >>> mmap, it has that sample_type.
    >
    >>> For record that means we need to dump each per-sample_id mmap onto a
    >>> separate file, i.e. use a directory, etc.
    >
    >> That seems like a major re-write of perf. Why not keep the existing
    >> restriction and have users who want different sample_types run
    >> multiple perf commands?
    >
    >> What's to be gained by refactoring the code to support multiple
    >> sample_types in a single command invocation?
    >
    > This comes from time to time:
    >
    > http://us.generation-nt.com/answer/bug-perf-event-sampling-buffer-format-cannot-handle-multi-event-sampling-help-202985832.html
    >
    > The whole point of sample_type is to ask for just what is needed for
    > some specific event so that we reduce the per sample footprint.
    >
    > So we allow for multiple types of events to be on the same stream, but
    > not for them to have just what each need, its a limitation, one that we
    > can solve. I see no reason not to solve it :-)
    >
    > The evsel/evlist classes were designed to abstract away such details,
    > i.e. perf_evlist__mmap should notice different sample_types and sort
    > this out transparently.
    >
    > And then perf_evlist__mmap_read(evlist, idx), evlist->nr_mmaps should be
    > enough to process the events :-)
    >
    > - Arnaldo

    An ABI change fixes the root cause of the current problem -- put an id
    in perf_event_header. The id maps to the evsel which has the
    sample_type. Right now you have to parse the sample to get the id to get
    the evsel.

    With that change I have a patch that (mostly?) covers the rest of perf
    userspace to handle sample_type per evsel.

    David


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