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Subject: Re: Ftrace: can trace kthread?
From: Peter Zijlstra <peterz@infradead.org>
To: "Figo.zhang" <zhangtianfei@leadcoretech.com>
Cc: Yong Zhang <yong.zhang0@gmail.com>, Li Zefan <lizf@cn.fujitsu.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Steven Rostedt <srostedt@redhat.com>
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Date: Thu, 21 Oct 2010 12:12:07 +0200
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On Thu, 2010-10-21 at 16:59 +0800, Figo.zhang wrote:
> > I just
> > echo  0 > tracing_enabled
> > echo function > current_tracer
> > echo 374(pid of flush) > set_ftrace_pid
> > echo 1 > tracing_enabled
> > wait some time
> > echo 0 > tracing_enabled
> > cat trace
> > 
> > So I think this answer your question "could kthread be traced?"
> 
> i do it the same of you.

> but i canot trace nothing. 

Your initial attempt had:

        echo kswapd > /sys/kernel/debug/tracing/set_graph_function

have you reset that state?