linux-kernel - Re: [PATCH 0/18] Allow different tracers to be compiled independently

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Date:	Mon, 22 Mar 2010 23:34:33 -0400
From:	Theodore Tso <tytso@....EDU>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Jan Kara <jack@...e.cz>, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Li Zefan <lizf@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/18] Allow different tracers to be compiled independently


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


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