[lttng-dev] [RFC PATCH 0/2] Identify UST threads by changing thread names

[Mathieu Desnoyers]

----- On Jun 3, 2016, at 8:11 AM, Jeremie Galarneau jeremie.galarneau at efficios.com wrote:

> And, of course, I forget to add Mathieu in CC... Coffee time!
> 
> Jérémie
> 
> On Fri, Jun 3, 2016 at 2:10 AM, Jérémie Galarneau
> <jeremie.galarneau at efficios.com> wrote:
>> Hi Raphaël,
>>
>> Adding Mathieu in CC. Please make sure you CC the maintainers when
>> submitting a patch.
>>
>> Regards,
>> Jérémie
>>
>> On Wed, Jun 1, 2016 at 11:04 AM, Raphaël Beamonte
>> <raphael.beamonte at gmail.com> wrote:
>>> Hi,
>>>
>>> I did not get any feedback about this, any thoughts ?
>>>
>>> Thanks,
>>> Raphaël
>>>
>>> 2016-04-21 16:50 GMT-04:00 Raphaël Beamonte <raphael.beamonte at gmail.com>:
>>>> Hi,
>>>>
>>>> This is an RFC patch for comments and ideas about how this should be
>>>> done. In recent work I've been doing, I found out that some UST-
>>>> instrumented userspace process was preempting itself. Looking further,
>>>> it was not the same TID, but the same process name. These processes
>>>> were LTTng-UST listener threads, but were not identified as so.
>>>> Adding a simple symbol, such as "-ust" or "-lttng" at the end of the
>>>> process name would help to identify such process directly in the
>>>> generated trace.
>>>>
>>>> You'll find below two different implementations with their pros
>>>> and cons, for which the "-ust" symbol was choosen:
>>>>
>>>>
>>>> 1/ An implementation using prctl
>>>>         It works properly on Linux, but I didn't find a way to make
>>>>         it work under FreeBSD, hence the empty function in FreeBSD
>>>>         case (keeping the situation as it is now).
>>>>
>>>> Raphaël Beamonte (1):
>>>>   Add -ust to the name of UST threads of the application
>>>>
>>>>  liblttng-ust/compat.h         | 22 ++++++++++++++++++++++
>>>>  liblttng-ust/lttng-ust-comm.c |  2 ++
>>>>  2 files changed, 24 insertions(+)
>>>>
>>>>
>>>>
>>>> 2/ An implementation using pthread
>>>>         It works on both Linux and FreeBSD, but requires to add a
>>>>         link to the pthread library in liblttng-ust Makefile.am.
>>>>         Also, this approach relies on the presence of the
>>>>         pthread_setname_np function, which was included in glibc
>>>>         2.12, meaning it will not work with older versions (but
>>>>         this should not be a problem?)

lttng-ust already uses libc for mutexes and other. So I don't see why
you have to _add_ any explicit dependency there.

About the glibc version, we should use autotools to detect the
features supported by the system libc, and pass a config define
to the source code, so we can use the glibc pthread_setname_np
if available, else we keep the current behavior.

Thoughts ?

Thanks,

Mathieu

>>>>
>>>> Raphaël Beamonte (1):
>>>>   Add -ust to the name of UST threads of the application
>>>>
>>>>  liblttng-ust/Makefile.am      |  1 +
>>>>  liblttng-ust/compat.h         | 35 +++++++++++++++++++++++++++++++++++
>>>>  liblttng-ust/lttng-ust-comm.c |  2 ++
>>>>  3 files changed, 38 insertions(+)
>>>>
>>>>
>>>>
>>>> I'll wait for your comments and ideas on that subject.
>>>>
>>>> Thanks,
>>>> Raphaël
>>>>
>>>>
>>>> --
>>>> 2.1.4
>>>>
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>>
>>
>>
>> --
>> Jérémie Galarneau
>> EfficiOS Inc.
>> http://www.efficios.com
> 
> 
> 
> --
> Jérémie Galarneau
> EfficiOS Inc.
> http://www.efficios.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com