linux-kernel - Re: [ftrace] possible to implement user-space tracers?

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Message-ID: <CAMKaFC-Hiefq+Nu+ejnKB63VGO7d9KOJqv_FomeejyBxOn_WPw@mail.gmail.com>
Date:	Wed, 12 Aug 2015 11:42:35 +0800
From:	Kun Huang <gareth@...nstacker.org>
To:	Scotty Bauer <sbauer@....utah.edu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [ftrace] possible to implement user-space tracers?

Hi Scotty

I have read your links. I found the read from 'trace' and the write to
'trace_marker' are normal read&write which works like proc system.

I have questions that what's more difference between ftrace and proc?
I just know I could read data as pipeline from ftrace.

On Wed, Aug 12, 2015 at 10:25 AM, Kun Huang <gareth@...nstacker.org> wrote:
> Thank you for your help Scotty :) I'm reading it.
>
> On Wed, Aug 12, 2015 at 2:34 AM, Scotty Bauer <sbauer@....utah.edu> wrote:
>> It is possible to trace from userland, Android does it.
>>
>> Essentially you need to write your data into
>> /sys/kernel/debug/tracing/trace_marker
>>
>> then read it out of /sys/kernel/debug/tracing/trace
>>
>>
>> If you care how the implementation works you can read it in
>> /kernel/tracing/trace.c
>> (http://lxr.free-electrons.com/source/kernel/trace/trace.c) search for
>> tracing_mark_fops and tracing_fops.
>>
>>
>> In Android here are the relevant files you will need to see how it's used in
>> userland:
>> Atrace (for reading data out + setting things up):
>> https://android.googlesource.com/platform/frameworks/native/+/master/cmds/atrace/atrace.cpp
>> https://android.googlesource.com/platform/external/chromium-trace/+/master
>> (host side setup of the device)
>>
>> trace-dev (for writing data in):
>> https://android.googlesource.com/platform/system/core/+/master/libcutils/trace-dev.c
>>
>> Once we have all the data we usually run it through trace-viewer,
>> (https://github.com/catapult-project/catapult)
>>
>> Cheers.
>>
>>
>>> On 2015-08-11 06:53, Kun Huang wrote:
>>>>
>>>> Hi ftrace developers
>>>>
>>>> I'm developing a huge python based programs and facing performance
>>>> issue everyday. I like the ftrace system and hope there could be a
>>>> tracer to trace&report my python codes. Is it possible or is it
>>>
>>> worthy
>>>>
>>>> to do this?
>>>>
>>>> ---
>>>>
>>>> Kun
>>>> --
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>>> [6]
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>>>> Please read the FAQ at  http://www.tux.org/lkml/ [7]
>>>
>>>
>>> Links:
>>> ------
>>> [1] http://lxr.free-electrons.com/source/kernel/trace/trace.c
>>> [2]
>>>
>>> https://android.googlesource.com/platform/frameworks/native/+/master/cmds/atrace/atrace.cpp
>>> [3]
>>> https://android.googlesource.com/platform/external/chromium-trace/+/master
>>> [4]
>>>
>>> https://android.googlesource.com/platform/system/core/+/master/libcutils/trace-dev.c
>>> [5] https://github.com/catapult-project/catapult
>>> [6] http://vger.kernel.org/majordomo-info.html
>>> [7] http://www.tux.org/lkml/
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