[Xenomai] Q: LTTNG & xenomai status

[Xenomai] Q: LTTNG & xenomai status

[Michael Haberler]

what is the status on using LTTNG tracepoints in an RT thread? the last
discussion has been a while back, like 2010ish

LTTNG 2.5.1 is in the debian jessie stream. Can I use that as-is?

Any special precautions I need to take, or do the stock instructions for
LTTNG apply?

thanks in advance,

Michael

Re: [Xenomai] Q: LTTNG & xenomai status

[Michael Haberler]

2015-03-26 23:37 GMT+01:00 Michael Haberler <haberlerm@gmail.com>:

> what is the status on using LTTNG tracepoints in an RT thread? the last
> discussion has been a while back, like 2010ish
>
> LTTNG 2.5.1 is in the debian jessie stream. Can I use that as-is?
>
> Any special precautions I need to take, or do the stock instructions for
> LTTNG apply?
>

noting that CONFIG_FTRACE was disabled for performance reasons:
http://www.xenomai.org/pipermail/xenomai/2013-January/027272.html

that would suggest *functionally* it is not an issue, and LTTng layers
ontop of CONFIG_FTRACE for kernel tracing

or am I overlooking something?


- Michael

(I know it is cramped style to follow up oneself, but I need to figure this
out for good so I'm not stuck later on)

> thanks in advance,
>
> Michael
>

Re: [Xenomai] Q: LTTNG & xenomai status

[Philippe Gerum]

On 03/30/2015 10:58 AM, Michael Haberler wrote:
> 2015-03-26 23:37 GMT+01:00 Michael Haberler <haberlerm@gmail.com>:
> 
>> what is the status on using LTTNG tracepoints in an RT thread? the last
>> discussion has been a while back, like 2010ish
>>
>> LTTNG 2.5.1 is in the debian jessie stream. Can I use that as-is?
>>
>> Any special precautions I need to take, or do the stock instructions for
>> LTTNG apply?
>>
> 
> noting that CONFIG_FTRACE was disabled for performance reasons:
> http://www.xenomai.org/pipermail/xenomai/2013-January/027272.html
> 
> that would suggest *functionally* it is not an issue, and LTTng layers
> ontop of CONFIG_FTRACE for kernel tracing
> 
> or am I overlooking something?
> 

Functionally it is not an issue, but the LTT core for any given LTT
version might not be entirely safe for running over a kernel with
pipelined interrupts. Fixing this is part of the usual process of
merging LTTng and the I-pipe.

-- 
Philippe.

Re: [Xenomai] Q: LTTNG & xenomai status

[Michael Haberler]

2015-03-30 11:17 GMT+02:00 Philippe Gerum <rpm@xenomai.org>:

> On 03/30/2015 10:58 AM, Michael Haberler wrote:
> > 2015-03-26 23:37 GMT+01:00 Michael Haberler <haberlerm@gmail.com>:
> >
> >> what is the status on using LTTNG tracepoints in an RT thread? the last
> >> discussion has been a while back, like 2010ish
> >>
> >> LTTNG 2.5.1 is in the debian jessie stream. Can I use that as-is?
> >>
> >> Any special precautions I need to take, or do the stock instructions for
> >> LTTNG apply?
> >>
> >
> > noting that CONFIG_FTRACE was disabled for performance reasons:
> > http://www.xenomai.org/pipermail/xenomai/2013-January/027272.html
> >
> > that would suggest *functionally* it is not an issue, and LTTng layers
> > ontop of CONFIG_FTRACE for kernel tracing
> >
> > or am I overlooking something?
> >
>
> Functionally it is not an issue, but the LTT core for any given LTT
> version might not be entirely safe for running over a kernel with
> pipelined interrupts. Fixing this is part of the usual process of
> merging LTTng and the I-pipe.
>

given that there is no code pertaining to LTTng in xenomai-2.6, I assume
you consider this the responsibility of the LTTng maintainers?

I will inquire on the lttng-dev list, but does "usual" imply they usually
take care of this?

- Michael



> --
> Philippe.
>

Re: [Xenomai] Q: LTTNG & xenomai status

[Philippe Gerum]

On 03/30/2015 11:51 AM, Michael Haberler wrote:
> 
> 
> 2015-03-30 11:17 GMT+02:00 Philippe Gerum <rpm@xenomai.org
> <mailto:rpm@xenomai.org>>:
> 
>     On 03/30/2015 10:58 AM, Michael Haberler wrote:
>     > 2015-03-26 23:37 GMT+01:00 Michael Haberler <haberlerm@gmail.com <mailto:haberlerm@gmail.com>>:
>     >
>     >> what is the status on using LTTNG tracepoints in an RT thread? the last
>     >> discussion has been a while back, like 2010ish
>     >>
>     >> LTTNG 2.5.1 is in the debian jessie stream. Can I use that as-is?
>     >>
>     >> Any special precautions I need to take, or do the stock instructions for
>     >> LTTNG apply?
>     >>
>     >
>     > noting that CONFIG_FTRACE was disabled for performance reasons:
>     > http://www.xenomai.org/pipermail/xenomai/2013-January/027272.html
>     >
>     > that would suggest *functionally* it is not an issue, and LTTng layers
>     > ontop of CONFIG_FTRACE for kernel tracing
>     >
>     > or am I overlooking something?
>     >
> 
>     Functionally it is not an issue, but the LTT core for any given LTT
>     version might not be entirely safe for running over a kernel with
>     pipelined interrupts. Fixing this is part of the usual process of
>     merging LTTng and the I-pipe.
> 
> 
> given that there is no code pertaining to LTTng in xenomai-2.6, I assume
> you consider this the responsibility of the LTTng maintainers?
> 
> I will inquire on the lttng-dev list, but does "usual" imply they
> usually take care of this?
>  

No, this implies that people have to take care of this when they need
it. By "usual", I mean "each time I had to do this".

-- 
Philippe.

Re: [Xenomai] Q: LTTNG & xenomai status

[Jan Kiszka]

On 2015-03-30 11:58, Philippe Gerum wrote:
> On 03/30/2015 11:51 AM, Michael Haberler wrote:
>>
>>
>> 2015-03-30 11:17 GMT+02:00 Philippe Gerum <rpm@xenomai.org
>> <mailto:rpm@xenomai.org>>:
>>
>>     On 03/30/2015 10:58 AM, Michael Haberler wrote:
>>     > 2015-03-26 23:37 GMT+01:00 Michael Haberler <haberlerm@gmail.com <mailto:haberlerm@gmail.com>>:
>>     >
>>     >> what is the status on using LTTNG tracepoints in an RT thread? the last
>>     >> discussion has been a while back, like 2010ish
>>     >>
>>     >> LTTNG 2.5.1 is in the debian jessie stream. Can I use that as-is?
>>     >>
>>     >> Any special precautions I need to take, or do the stock instructions for
>>     >> LTTNG apply?
>>     >>
>>     >
>>     > noting that CONFIG_FTRACE was disabled for performance reasons:
>>     > http://www.xenomai.org/pipermail/xenomai/2013-January/027272.html
>>     >
>>     > that would suggest *functionally* it is not an issue, and LTTng layers
>>     > ontop of CONFIG_FTRACE for kernel tracing
>>     >
>>     > or am I overlooking something?
>>     >
>>
>>     Functionally it is not an issue, but the LTT core for any given LTT
>>     version might not be entirely safe for running over a kernel with
>>     pipelined interrupts. Fixing this is part of the usual process of
>>     merging LTTng and the I-pipe.
>>
>>
>> given that there is no code pertaining to LTTng in xenomai-2.6, I assume
>> you consider this the responsibility of the LTTng maintainers?
>>
>> I will inquire on the lttng-dev list, but does "usual" imply they
>> usually take care of this?
>>  
> 
> No, this implies that people have to take care of this when they need
> it. By "usual", I mean "each time I had to do this".
> 

We used to integrate Xenomai with LTTng back then but gave up as LTTng
made no progress towards upstream and the efforts became too high. These
days you get Xenomai kernel instrumentation via ftrace, at least in 3.0.
Maybe give that a try first and then tell us what is missing.

For 2.6, we have some out-of-tree ftrace patches for x86-64 as well. Can
refresh our queue [1] if needed.

Jan

[1] http://git.xenomai.org/xenomai-jki.git/log/?h=queues/ftrace

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Re: [Xenomai] Q: LTTNG & xenomai status

[Michael Haberler]

2015-03-30 18:11 GMT+02:00 Jan Kiszka <jan.kiszka@web.de>:

> On 2015-03-30 11:58, Philippe Gerum wrote:
> > On 03/30/2015 11:51 AM, Michael Haberler wrote:
> >>
> >>
> >> 2015-03-30 11:17 GMT+02:00 Philippe Gerum <rpm@xenomai.org
> >> <mailto:rpm@xenomai.org>>:
> >>
> >>     On 03/30/2015 10:58 AM, Michael Haberler wrote:
> >>     > 2015-03-26 23:37 GMT+01:00 Michael Haberler <haberlerm@gmail.com
> <mailto:haberlerm@gmail.com>>:
> >>     >
> >>     >> what is the status on using LTTNG tracepoints in an RT thread?
> the last
> >>     >> discussion has been a while back, like 2010ish
> >>     >>
> >>     >> LTTNG 2.5.1 is in the debian jessie stream. Can I use that as-is?
> >>     >>
> >>     >> Any special precautions I need to take, or do the stock
> instructions for
> >>     >> LTTNG apply?
> >>     >>
> >>     >
> >>     > noting that CONFIG_FTRACE was disabled for performance reasons:
> >>     > http://www.xenomai.org/pipermail/xenomai/2013-January/027272.html
> >>     >
> >>     > that would suggest *functionally* it is not an issue, and LTTng
> layers
> >>     > ontop of CONFIG_FTRACE for kernel tracing
> >>     >
> >>     > or am I overlooking something?
> >>     >
> >>
> >>     Functionally it is not an issue, but the LTT core for any given LTT
> >>     version might not be entirely safe for running over a kernel with
> >>     pipelined interrupts. Fixing this is part of the usual process of
> >>     merging LTTng and the I-pipe.
> >>
> >>
> >> given that there is no code pertaining to LTTng in xenomai-2.6, I assume
> >> you consider this the responsibility of the LTTng maintainers?
> >>
> >> I will inquire on the lttng-dev list, but does "usual" imply they
> >> usually take care of this?
> >>
> >
> > No, this implies that people have to take care of this when they need
> > it. By "usual", I mean "each time I had to do this".
> >
>
> We used to integrate Xenomai with LTTng back then but gave up as LTTng
> made no progress towards upstream and the efforts became too high. These
> days you get Xenomai kernel instrumentation via ftrace, at least in 3.0.
> Maybe give that a try first and then tell us what is missing.
>

the kernel tracing would be nice to have and if ftrace covers that - fine

I'm primarily interested in userland tracing (lttng-ust) - it would be nice
to have that merged with kernel tracing into a unified view as LTTng does
it but if not, I'll live with that

this still leaves open the question if LTTng userspace tracing intervenes
somehow with Xenomai userland threads
the ringbuffer event notification comes to my mind, I think it is an
(optional, can be suppressed) write to a pipe

- Michael


>
> For 2.6, we have some out-of-tree ftrace patches for x86-64 as well. Can
> refresh our queue [1] if needed.
>
> Jan
>
> [1] http://git.xenomai.org/xenomai-jki.git/log/?h=queues/ftrace
>
>