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Date: Tue, 23 Mar 2010 02:04:21 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: 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>
Cc: LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/18] Allow different tracers to be compiled
	independently
Message-ID: <20100323010419.GA8292@nowhere>
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On Tue, Mar 23, 2010 at 01:32:02AM +0100, Jan Kara wrote:
> 
>   Hi,
> 
>   currently, when one tracer is selected, most of tracepoints for other
> tracers also gets pulled into the kernel. So for example it's not possible
> to enable BLK_DEV_IO_TRACE without polluting slab allocation paths with
> tracepoint checks (see changelog of patch 01). This patch set adds a
> possibility for each set of trace points to be compile-enabled separately.
>   The first patch contains the necessary magic in linux/tracepoint.h. Other
> patches just tell tracing framework about correspoding config options
> and possibly introduce them if they did not exist before.
>   The patches in this patch set are actually completely independent so 
> they can be merged via respective subsystem trees. But changes are rather
> tiny so I don't expect much conflicts...
> 
> 								Honza


(Adding more people in Cc)

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...

I wonder if this is going to be a win.