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

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Date:	Tue, 16 Sep 2014 19:58:34 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Pawel Moll <pawel.moll@....com>
Cc:	David Ahern <dsahern@...il.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Richard Cochran <richardcochran@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	John Stultz <john.stultz@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [RFC 2/2] perf: Marker software event and ioctl


* Pawel Moll <pawel.moll@....com> wrote:

> 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 ;-)

Well, it's a user-space generated trace/event entry, so lets call 
it that?

Thanks,

	Ingo
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