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Subject: Re: [PATCH 0/18] Allow different tracers to be compiled independently
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From: Theodore Tso <tytso@MIT.EDU>
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Date: Mon, 22 Mar 2010 23:34:33 -0400
Cc: Jan Kara <jack@suse.cz>, Steven Rostedt <rostedt@goodmis.org>,
       Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       Li Zefan <lizf@cn.fujitsu.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Masami Hiramatsu <mhiramat@redhat.com>,
       Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
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To: Frederic Weisbecker <fweisbec@gmail.com>
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On Mar 22, 2010, at 9:04 PM, Frederic Weisbecker wrote:
> 
> I don't know. Yeah this first looks like a good idea but once
> CONFIG_EVENT_TRACING is enabled, each tracepoint is a lightweight
> thing and induce a tiny overhead, probably hard to notice, and
> this is going to be even more the case after the jmp label
> optimization patches.
> 
> I liked the fact we had a general tracing kernel once the above
> config is selected. And we don't bother telling people that to
> use tool X you need CONFIG_EVENT_Y, and you need to rebuild your
> kernel, etc...

Indeed, a lot of the value of tracepoints goes away if people are compiling kernels without them and we need to get a special "tracing kernel" installed before we can debug a problem.

So I'd hope we can do the necessary optimization work so people don't feel it's necessary to enable or disable tracepoints by subsystem....

-- Ted