linux-kernel - Re: [PATCH 21/21] tracing: Add optional percpu buffers for trace

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Date:	Fri, 23 Sep 2011 13:02:02 +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>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 21/21] tracing: Add optional percpu buffers for
 trace_printk()

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? #$%@^%@@$%@
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