Re: [RFC 2/2] perf: Marker software event and ioctl

From: Pawel Moll
Date: Tue Sep 16 2014 - 12:38:01 EST

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 ;-)


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