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

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Message-ID: <AANLkTinkMrsRQ8tdCrTj57SA_qHYrg+-qCqZpyQZ-FMr@mail.gmail.com>
Date:	Thu, 21 Oct 2010 17:08:51 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	"Figo.zhang" <zhangtianfei@...dcoretech.com>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: Ftrace: can trace kthread?

On Thu, Oct 21, 2010 at 4:59 PM, Figo.zhang
<zhangtianfei@...dcoretech.com> 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.
>
> [root@...ost tracing]# ps -ax | grep flush
> Warning: bad ps syntax, perhaps a bogus '-'? See http://procps.sf.net/faq.html
>  1205 ?        S      0:01 [flush-8:0]
> 11852 pts/1    S+     0:00 grep flush
> [root@...ost tracing]#
>
> so my flusher pid is 1205, i do it as below:
>
> [root@...ost tracing]# echo 0 > tracing_enabled
> [root@...ost tracing]# echo function > current_tracer
> [root@...ost tracing]# echo 1205 > set_ftrace_pid
> [root@...ost tracing]# echo 1 > tracing_enabled
>
> wait ... and open some pdf files, let system eat huge memory...
>
> [root@...ost tracing]# echo 0 > tracing_enabled
> [root@...ost tracing]# cat trace
> # tracer: function
> #
> #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
> #              | |       |          |         |
>
>
> but i canot trace nothing.

Is tracing_on enable(1) on your system?
I enable it on my system by default, so I didn't show it in the previous mail.

Thanks,
Yong
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