linux-kernel - Re: perf/tracepoints access to interpreted strings

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Message-ID: <20150421090733.3a6cc742@gandalf.local.home>
Date:	Tue, 21 Apr 2015 09:07:33 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	David Ahern <dsahern@...il.com>
Cc:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
	Namhyung Kim <namhyung@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf/tracepoints access to interpreted strings

On Mon, 20 Apr 2015 15:26:56 -0600
David Ahern <dsahern@...il.com> wrote:

> On 4/20/15 3:25 PM, Arnaldo Carvalho de Melo wrote:
> > Em Mon, Apr 20, 2015 at 04:46:16PM -0400, Steven Rostedt escreveu:
> >> On Wed, 15 Apr 2015 15:09:27 -0300
> >> Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> >>> If it is strictly an enum, i.e. no holes and just by looking at the
> >>> "format" file above I don't see how it could have holes, albeit enums
> >>> may have, we can as well have this:
> >
> >>> 	const char *perf_evsel__enum(struct perf_evsel *evsel,
> >>> 				     struct perf_sample *sample,
> >>> 				     const char *enum_name);
> >
> >>> That would return an array of strings that you could directly access,
> >>> indexing using some of the fields.
> >
> >>> I.e. internally we would see the tracepoint format file as:
> >
> >>>   	field:enum action vec;	offset:12;	size:4;	signed:0;
> >
> >>> 	enum: action: TIMER, NET_TX, NET_RX, BLOCK, BLOCK_IOPOLL, TASKLET, SCHED, HRTIMER, RCU
> >
> >> Note, with the new TRACE_DEFINE_ENUM() that was already added to
> >> Linus's tree, that print_fmt now looks like:
> >
> >> print fmt: "vec=%u [action=%s]", REC->vec, __print_symbolic(REC->vec,
> >>   { 0, "HI" }, { 1, "TIMER" }, { 2, "NET_TX" }, { 3, "NET_RX" }, { 4, "BLOCK" },
> >>   { 5, "BLOCK_IOPOLL" }, { 6, "TASKLET" }, { 7, "SCHED" }, { 8, "HRTIMER" },
> >>   { 9, "RCU" })
> >
> > That is better, indeed, covers holes :-)
> 
> Seems to me that means 2 different implementations are needed ... old 
> and new.

Why? The above is the way most trace points use __print_symbolic().
It's just when a tracepoint uses enums instead of defines or hard coded
numbers do the useless enum name pops up.

Any parse should be expecting numbers, not enum names.

-- Steve
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