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Subject: Re: Ftrace: can trace kthread?
From: "Figo.zhang" <zhangtianfei@leadcoretech.com>
To: Yong Zhang <yong.zhang0@gmail.com>
Cc: 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 16:59:02 +0800
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> 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@myhost 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@myhost tracing]# 

so my flusher pid is 1205, i do it as below:

[root@myhost tracing]# echo 0 > tracing_enabled 
[root@myhost tracing]# echo function > current_tracer
[root@myhost tracing]# echo 1205 > set_ftrace_pid 
[root@myhost tracing]# echo 1 > tracing_enabled 

wait ... and open some pdf files, let system eat huge memory...

[root@myhost tracing]# echo 0 > tracing_enabled 
[root@myhost tracing]# cat trace
# tracer: function
#
#           TASK-PID    CPU#    TIMESTAMP  FUNCTION
#              | |       |          |         |


but i canot trace nothing.