From mboxrd@z Thu Jan  1 00:00:00 1970
From: Pawel Moll <pawel.moll-5wv7dgnIgG8@public.gmane.org>
Subject: Re: [RFC 2/2] perf: Marker software event and ioctl
Date: Tue, 16 Sep 2014 17:37:43 +0100
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Cc: David Ahern <dsahern-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Arnaldo Carvalho de Melo <acme-f8uhVLnGfZaxAyOMLChx1axOck334EZe@public.gmane.org>, Richard Cochran <richardcochran-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>, Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Paul Mackerras <paulus-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org>, John Stultz <john.stultz-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
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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