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

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Message-ID: <1289998957.2109.751.camel@laptop>
Date:	Wed, 17 Nov 2010 14:02:37 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	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>,
	Steven Rostedt <rostedt@...dmis.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 13:53 +0100, Frederic Weisbecker wrote:
> On Wed, Nov 17, 2010 at 12:35:50PM +0100, Peter Zijlstra wrote:
> > On Wed, 2010-11-17 at 09:30 +0100, Ingo Molnar wrote:
> > > > For example I'm currently working with dozens of trace_printk() and I would be 
> > > > very happy to turn some of them off half of the time.
> > > 
> > > I guess we could try such a patch. If you send a prototype i'd be interested in 
> > > testing it out.
> > 
> > I don't see the point, the kernel shouldn't contain any trace_printk()s
> > to begin with..
> 
> 
> It's oriented toward developers. Those who use dozens of tracepoints in
> their tree because they are debugging something or developing a new feature,
> they might to deactivate/reactivate some of these independant points.
> 
> This can also apply to dynamic_printk of course.
> 
> Well, the very first and main point is to standardize trace_printk into
> a trace event so that it gets usable by perf tools. I have been asked many
> times "how to use trace_printk() with perf?".

Thing is, since its these dev who add the trace_printk()s to begin with,
I don't see the point in splitting them out, if you didn't want them why
did you add them to begin with?!

As to the trace_printk() to perf interface, you could do like mingo did
and create a fake event and use the regular tracepoint interface, or
hook it up directly and create a PERF_RECORD_TEXT field.

Personally I like the trace_printk() as a TRACE_EVENT(printk), it also
allows removing lots of the special casing concerning trace_printk from
ftrace.


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