linux-kernel - Re: [PATCH 2/3][RFC] tracing: Add optional percpu buffers for trace

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Date:	Mon, 10 Oct 2011 13:08:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 2/3][RFC] tracing: Add optional percpu buffers for
 trace_printk()

On Sat, 2011-10-08 at 13:02 -0400, Steven Rostedt wrote:
> 
> Ideally, using percpu buffers would be useful, but since trace_printk()
> is only used in development, having per cpu buffers for something
> never used is a waste of space. We could make this a compile option
> but trace_printk() may also be used for developing modules, on a
> distro kernels or for debugging at customer sites.
> 
> The approach taken here is to dynamically allocate percpu buffers
> with a new tracing/options switch "trace_printk_percpu". It can
> be allocated and freed at runtime, or "trace_printk_percpu" may also
> be specified on the command line and it will be allocated at boot up.
> 
> This allows a developer to create percpu buffers for trace_printk()
> on a running system, and also free them when not in used. 

Kill the old code, make tracing/events/trace_printk default to 0 and use
enabling of that to allocate your per-cpu buffers.



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