linux-kernel - Re: [PATCH] tracing/ftrace: use preempt_enable_no_resched_notrace in ring_buffer_time

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Message-ID: <alpine.DEB.1.10.0812161752040.25356@gandalf.stny.rr.com>
Date:	Tue, 16 Dec 2008 17:53:13 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Frédéric Weisbecker <fweisbec@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/ftrace: use preempt_enable_no_resched_notrace
 in ring_buffer_time_stamp()


On Tue, 16 Dec 2008, Ingo Molnar wrote:
> 
> i noticed high stack-tracer overhead too. Which is understandable i guess: 
> the stack tracer keeps the mcount callbacks running all the time and can 
> save the stack backtrace of the highest-stack-usage point in time that the 
> kernel ever has hit in the past. That is a pretty powerful debug 
> capability, with appropriate costs.

I was thinking of having a way to start and stop the stack tracer. This 
way we can actually have it on by default with anything that has dynamic 
ftace. To enable it durning boot would require a kernel command line 
option. Other than that, I would have a sysctl enable it.

-- Steve

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