Subject: Re: [ANNOUNCE] New utility: 'trace'
From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, Darren Hart <dvhart@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Arjan van de Ven <arjan@infradead.org>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Tom Zanussi <tzanussi@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Li Zefan <lizf@cn.fujitsu.com>, Jason Baron <jbaron@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Christoph Hellwig <hch@lst.de>, Pekka Enberg <penberg@kernel.org>,
        Lai Jiangshan <laijs@cn.fujitsu.com>,
        Eric Dumazet <eric.dumazet@gmail.com>
In-Reply-To: <20101117125344.GC5464@nowhere>
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Date: Wed, 17 Nov 2010 14:02:37 +0100
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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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