linux-kernel - Re: [PATCH 2/2][RFC] tracing: Add extract out softirq names used by irq trace events

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Message-ID: <1267151179.6328.86.camel@gandalf.stny.rr.com>
Date:	Thu, 25 Feb 2010 21:26:19 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Li Zefan <lizf@...fujitsu.com>, Christoph Hellwig <hch@....de>,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [PATCH 2/2][RFC] tracing: Add extract out softirq names used
 by irq trace events

On Fri, 2010-02-26 at 00:48 +0100, Frederic Weisbecker wrote:

> 
> And what about a kind of macro that could have two effects:
> 
> - define the enum
> - define the nr -> name pairs for resolution
> 
> This could be something like:
> 
> define_trace_enum(softirq)
> 	enum_entry(TASKLET, 4), //don't know if it's 4, just an example
> 	enum_entry(HRTIMER, 5),
> end_trace_enum()

That wont work. Unless it is in a separate file that can be included
over and over again. That is we would need:

** include/linux/softirq_names.h:

define_trace_enum(softirq)
	enum_entry(HI, 0),
	enum_entry(TIMER, 1),
	[...]
end_trace_enum();



** include/trace/define_enum.h:

#define define_trace_enum(name)  enum name {
#define enum_entry(a, b)  a = b
#define end_trace_enum()  }


** include/linux/interrupt.h

/* instead of declaring an enum we have */

#include <trace/define_enum.h>
#include <linux/softirq_names.h>

Here we could do something special with that file.

> 
> (My naming sucks, as usual).
> 
> In normal headers, it would define an enum:
> 
> enum softirq {
> 	TASKLET = 4,
> 	HRTIMER = 5,
> };
> 
> And in the file that has DEFINE_TRACEPOINT:
> 
> /* can be in ftrace_event.h */
> struct resolve_enum {
> 	const char *name;
> 	int val;
> };
> 
> struct resolve_enum softirq = { //come from define_trace_enum()
> 	{"TASKLET", 4}, //come from enum_entry()
> 	{"HRTIMER", 5},
> 	{ NULL, 0}, /* end */
> };
> 
> /* This can be used from the trace_event macro */
> const char *softirq_name(int nr)
> {
> 	return resolve_enum[nr];
> }
> 
> 
> And then you can get back the struct resolve_enum softirq
> to export the values to debugfs, may be by storing such
> structures in a section (and adding the name of the enum)
> 
> This has the advantage of beeing sync with core header
> changes, but this has the drawback of beeing less readable
> to define an enum usable from a TRACE_EVENT (especially
> if I define the naming personally).
> 


This just gets ugly and I'm not sure people would like doing this. It
also requires that you number the enums specifically.

A better way could be this:

** include/linux/interrupt.h

#define SOFTIRQ_NAMES 	\
	C(HI),		\
	C(TIMER),	\
	[...]		\
	C(RCU)

#define C(name)		name##_SOFTIRQ

enum { SOFTIRQ_NAMES, NR_SOFTIRQS };

#undef C

And in the trace file we could do:

#define C(name)  { #name, name##_SOFTIRQ, sizeof(name##_SOFTIRQ) }

struct {
	char *name;
	int val;
	int size;
} softirq_names[] __attribute__((section("trace_syms"))) =
  { SOFTIRQ_NAMES };

#undef C


This way we don't need to number every enum, or have to move the enum
into another file. My question is...

Would the following be acceptable in normal headers?

#define ENUM_NAMES  	\
	C(a),		\
	C(b),		\
	...

#define C(name) name

enum { ENUM_NAMES };

#undef C

-- Steve


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