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    SubjectRe: [RFC 2/2] perf: Marker software event and ioctl
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    On Tue, 2014-09-16 at 08:44 +0100, Ingo Molnar wrote:
    > I think adding an ioctl to inject user-provided data into the
    > event stream is sensible, as long as there's a separate 'user
    > generated data' event for it, etc.
    >
    > The main usecase I could see would be to introduce a
    > perf_printf() variant, supported by 'perf trace' by default, to
    > add various tracable printouts to apps.
    >
    > Timestamps generated by apps would be another usecase. It would
    > probably be wise to add a 32-bit (or 64-bit) message type ID,
    > plus a length field, with a message type registry somewhere in
    > tools/perf/ (and reference implementation for each new subtype),
    > to keep things organized yet flexible going forward.

    Right, so this is pretty much what I got talking to Arnaldo...

    > { u64 type; /* 0 means zero-terminated string in data */
    > u32 size;
    > char data[size]; } && PERF_SAMPLE_MARKER

    ... with one type - 0 - defined as a "universal" string (so any possible
    tool knows what to do about it), the rest being left to userspace (this
    "registry" you mention).

    Before I proceed any further, is the term "marker" acceptable? Maybe a
    "printf" instead? Or a "log"? As we know naming is often single most
    discussed subject when it comes to new things in the kernel ;-)

    Pawel



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