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Subject: Re: [PATCH 21/21] tracing: Add optional percpu buffers for
 trace_printk()
From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
        Andrew Morton <akpm@linux-foundation.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 23 Sep 2011 13:02:02 +0200
In-Reply-To: <20110922221030.111078233@goodmis.org>
References: <20110922220935.537134016@goodmis.org>
	 <20110922221030.111078233@goodmis.org>
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On Thu, 2011-09-22 at 18:09 -0400, Steven Rostedt wrote:
> 
> Currently, trace_printk() uses a single buffer to write into
> to calculate the size and format needed to save the trace. To
> do this safely in an SMP environment, a spin_lock() is taken
> to only allow one writer at a time to the buffer. But this could
> also affect what is being traced, and add synchronization that
> would not be there otherwise. 

so trace_printk() isn't NMI safe? #$%@^%@@$%@