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

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Message-ID: <AANLkTi=D_a_BH-HW9mqwLim+DjxARWzT8mxP_dah5iLY@mail.gmail.com>
Date:	Thu, 21 Oct 2010 16:54:25 +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 4:44 PM, Figo.zhang
<zhangtianfei@...dcoretech.com> wrote:
>
>> > i try by set_ftrace_pid, it also can't ftrace the kswapd.
>>
>> Are you sure kswapd got chance to run on your system?
>>
>> BTW, I can successfully trace bdi_writeback_thread,
>> # tracer: function
>> #
>> #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
>> #              | |       |          |         |
>>        flush-8:0-374   [000] 600743.828496: finish_task_switch <-schedule
>>        flush-8:0-374   [000] 600743.828498: perf_event_task_sched_in
>> <-finish_task_switch
>>        flush-8:0-374   [000] 600743.828498: del_timer_sync <-schedule_timeout
>>        flush-8:0-374   [000] 600743.828499: try_to_del_timer_sync
>> <-del_timer_sync
>>        flush-8:0-374   [000] 600743.828499: lock_timer_base
>> <-try_to_del_timer_sync
>>        flush-8:0-374   [000] 600743.828499: _spin_lock_irqsave <-lock_timer_base
>>        flush-8:0-374   [000] 600743.828500: _spin_unlock_irqrestore
>> <-try_to_del_timer_sync
>>        flush-8:0-374   [000] 600743.828500: kthread_should_stop
>> <-bdi_writeback_task
>
> are you use my scprit to trace the bdi_writeback_thread ?

No.

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?"

Thanks,
Yong
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