linux-kernel - Re: Ftrace: can trace kthread?

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Date:	Thu, 21 Oct 2010 09:31:41 -0400
From:	Steven Rostedt <srostedt@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>, rostedt@...dmis.org
Cc:	"Figo.zhang" <zhangtianfei@...dcoretech.com>,
	Yong Zhang <yong.zhang0@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Ftrace: can trace kthread?

On Thu, 2010-10-21 at 12:12 +0200, Peter Zijlstra wrote:
> On Thu, 2010-10-21 at 16:59 +0800, Figo.zhang wrote:
> > > I just
> > > echo  0 > tracing_enabled

I need to remove that file. "tracing_enabled" is pretty much deprecated,
just use tracing_on to enable and disable the trace recording.

> > > 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

Yeah, that wont work. That's because kswapd() is called at system
startup and goes into a loop. The function graph tracer will never see
that function again (it's not called again). It can't know what function
it is in, only what functions it enters.

-- Steve

> 
> have you reset that state?


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