linux-kernel - Re: [ANNOUNCE] New utility: 'trace'

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Date:	Wed, 17 Nov 2010 10:02:41 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Darren Hart <dvhart@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Jason Baron <jbaron@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Christoph Hellwig <hch@....de>,
	Pekka Enberg <penberg@...nel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [ANNOUNCE] New utility: 'trace'

On Wed, 2010-11-17 at 15:10 +0100, Frederic Weisbecker wrote:

> Yeah I have a strange workflow. I'm working on that CPU isolation thing
> and I have dozens of trace_printk all over the place for tons of
> things. And everytime I remove one to unwind some output or to focus
> on another one, I often have to restore it later because I need it
> again. Usually I even just comment it out instead of removing it.
> 
> If I could make this dynamically on a per line filtering, or sometimes on
> a per file granularity (as both are equally often the case for me), I would
> probably win some time.
> 
> I just don't know how many developers have a similar workflow than mine.

I usually wrap trace_printk() (or printk sometimes) in my own wrapper:

#define sprintk(on, x...) do { if (on) { trace_prinkt(x); } } while (0)

Then have things like:

#define SDR_DEBUG_IRQS 0
#define SDR_DEBUG_SCHED 1
[...]

and in the irq code I'll have:

	sprintk(SDR_DEBUG_IRQS, "printme"...);

and the sched code:

	sprintk(SDR_DEBUG_SCHED, "printthis"...);

And I can easily enable or disable the prints I want. Sometimes I'll
define it as a variable, and enable them either in certain code paths,
or export them in the debugfs system and enable or disable them from
userspace.

extern int sdr_debug_irqs;
#define SDR_DEBUG_IRQS sdr_debug_irqs

[...]
int sdr_debug_irqs;
[...]

	debugfs_create_bool("sdr_debug_sched", 0644, NULL, &sdr_debug_irqs);

Of course this is all for temporary debugging. I use SDR and sdr and
sprintk to search and delete the debugging output when done.

-- Steve


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