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

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Message-ID: <20100323080526.GB4848@elte.hu>
Date:	Tue, 23 Mar 2010 09:05:26 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Theodore Tso <tytso@....EDU>
Cc:	Frederic Weisbecker <fweisbec@...il.com>, Jan Kara <jack@...e.cz>,
	Steven Rostedt <rostedt@...dmis.org>,
	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


* Theodore Tso <tytso@....EDU> wrote:

> 
> 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....

Yeah, agreed. Ultra-embedded can disable them all, but other than that i think 
we should not make it too finegrained as a lot of tooling value is in the 
'critical mass' that tracepoints have achieved. The power events tracepoints 
are most useful when combined with scheduling events, etc.

	Ingo
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