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

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Date:	Tue, 16 Sep 2014 17:37:43 +0100
From:	Pawel Moll <pawel.moll@....com>
To:	Ingo Molnar <mingo@...nel.org>
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

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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