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boundary="===============7721089565356983973==" Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" --===============7721089565356983973== Content-Language: fr-FR Content-Type: multipart/alternative; boundary="_000_AM7PR02MB6194C2E06B14077092AA06A0D12A9AM7PR02MB6194eurp_" --_000_AM7PR02MB6194C2E06B14077092AA06A0D12A9AM7PR02MB6194eurp_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi Norbert, Thank you for your answer ! Yes, I am using a Xenomai cobalt - xenomai is 3.1 cat /proc/xenomai/version =3D> 3.1 After the installation, I tested "test tools" in /proc/xenomai/ and it work= ed nice. What do you mean by "it might deadlock really good" ? Cheers, ________________________________ De : Norbert Lange Envoy=E9 : jeudi 20 mai 2021 10:20 =C0 : MONTET Julien Cc : lttng-dev@lists.lttng.org Objet : Re: [lttng-dev] LTTng - Xenomai : different results between timesta= mp-lttng and rt_time_read() Am Do., 20. Mai 2021 um 09:58 Uhr schrieb MONTET Julien via lttng-dev : > > Hi the developers ! > > CONTEXT > I am currently working on a Raspberry pi 3B with Xenomai and LTTng tools. > Raspbian 10.9 Buster - kernel 4.19.85 > uname -a : Linux raspberrypi 4.19.85-v7+ #5 SMP PREEMPT Wed May 12 10:13:= 37 > Both tools are working, but I wonder about the accuracy of LTTng librarie= s. > > > METHOD > The code used is quite simple, it is written with the alchemy skin. > A rt_task_spawn calls a function that has rt_task_set_periodic(NULL, TM_N= OW, period) and rt_task_wait_period(NULL). > ->The rt_task_set_periodic is based on 1ms. > ->The rt_task_wait_period(NULL) is of course inside a while loop (see be= low at the very end). > > My goal is to get accurate traces from Xenomai. > I took two methods to do so : > -> lttng > -> basic calculation based on rt_timer_read() > > What a surprise when I found both method have two different results. > -> LTTng shows me traces [0.870;1.13] ms (or even less precise) > -> rt_time_read shows me traces [0.980;1.020] ms > > Thing to note : > -> The use of LTTng has no influence on rt_time_read(), you can use both = methods at the same time. > > Then, I saved the output of rt_time_read inside a tracepoint. > It appeared the LTTng is always called at the right time because the valu= e got by rt_time_read () is really good. > > > QUESTIONS > These are now my questions : > - What is the method I should trust ? > - I have searched on the forum and I found LTTng uses a MONOTONIC clock f= or the timestamp. Can/Should I modify it ? > > > CODE > ----------------------------------------------------------------------- > A small part of my function called by rt_task_spawn : > [...] > RTIME period =3D 1000*1000; // in ns > RTIME now; > RTIME previous =3D 0; > RTIME duration; > [...] > while(1) > { > overruns =3D 0; > err =3D rt_task_wait_period(&overruns); > now =3D rt_timer_read(); > tracepoint(tp_provider, tracepoint_tick_ms, now, "tick"); > > if (previous !=3D 0) > { > duration=3Dnow-previous; > rt_printf("%llu\n \n", duration/1000); > } > previous=3Dnow; > [...] > } Are you using the Xenomai kernel ("Cobalt"), or just skins via copperplate ("Mercury")? You have some file /proc/xenomai/version? The Xenomai kernel has his own clock, which in general is not correlated to the linux monotonic clock. (Under some circumstances it might be identical). My plan is to use a clock plugin for Lttng, particularly because if lttng uses the linux monotonic clock from a realtime thread it might deadlock really good ;) Norbert --_000_AM7PR02MB6194C2E06B14077092AA06A0D12A9AM7PR02MB6194eurp_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Hi Norbert,

Thank you for your answer !

Yes, I am using a Xenomai cobalt - xenomai is 3.1
= cat /proc/xenomai/version =3D> 3.1
=
After the installation, I tested "test tools" in /proc/xe= nomai/ and it worked nice.

What do you mean by "it might deadlock really good" ?

Cheers,

De : Norbert Lange <nola= nge79@gmail.com>
Envoy=E9 : jeudi 20 mai 2021 10:20
=C0 : MONTET Julien <julien.montet@reseau.eseo.fr>
Cc : lttng-dev@lists.lttng.org <lttng-dev@lists.lttng.org>= ;
Objet : Re: [lttng-dev] LTTng - Xenomai : different results between = timestamp-lttng and rt_time_read()
 
Am Do., 20. Mai 2021 um 09:58 Uhr schrieb MONTET J= ulien via lttng-dev
<lttng-dev@lists.lttng.org>:
>
> Hi the developers !
>
> CONTEXT
> I am currently working on a Raspberry pi 3B with Xenomai and LTTng too= ls.
> Raspbian 10.9 Buster - kernel 4.19.85
> uname -a : Linux raspberrypi 4.19.85-v7+ #5 SMP PREEMPT Wed May 12 10:= 13:37
> Both tools are working, but I wonder about the accuracy of LTTng libra= ries.
>
>
> METHOD
> The code used is quite simple, it is written with the alchemy skin. > A rt_task_spawn calls a function that has rt_task_set_periodic(NULL, T= M_NOW, period) and rt_task_wait_period(NULL).
> ->The rt_task_set_periodic is based on 1ms.
> ->The  rt_task_wait_period(NULL) is of course inside a while l= oop (see below at the very end).
>
> My goal is to get accurate traces from Xenomai.
> I took two methods to do so :
> -> lttng
> -> basic calculation based on  rt_timer_read()
>
> What a surprise when I found both method have two different results. > -> LTTng shows me traces [0.870;1.13] ms (or even less precise)
> -> rt_time_read shows me traces [0.980;1.020] ms
>
> Thing to note :
> -> The use of LTTng has no influence on rt_time_read(), you can use= both methods at the same time.
>
> Then, I saved the output of rt_time_read inside a tracepoint.
> It appeared the LTTng is always called at the right time because the v= alue got by rt_time_read () is really good.
>
>
> QUESTIONS
> These are now my questions :
> - What is the method I should trust ?
> - I have searched on the forum and I found LTTng uses a MONOTONIC cloc= k for the timestamp. Can/Should I modify it ?
>
>
> CODE
> ----------------------------------------------------------------------= -
> A small part of my function called by rt_task_spawn :
> [...]
>     RTIME period =3D 1000*1000; // in ns
>     RTIME now;
>     RTIME previous =3D 0;
>     RTIME duration;
> [...]
>  while(1)
>     {
>         overruns =3D 0;
>         err =3D rt_task_wait_p= eriod(&overruns);
>         now =3D rt_timer_read(= );
>         tracepoint(tp_provider= , tracepoint_tick_ms, now, "tick");
>
>         if (previous !=3D 0) >         {
>            = ; duration=3Dnow-previous;
>            = ; rt_printf("%llu\n \n", duration/1000);
>         }
>        previous=3Dnow;
>    [...]
> }

Are you using the Xenomai kernel ("Cobalt"), or just skins via copperplate ("Mercury")?
You have some file /proc/xenomai/version?

The Xenomai kernel has his own clock, which in general is not
correlated to the linux monotonic clock.
(Under some circumstances it might be identical).

My plan is to use a clock plugin for Lttng, particularly because if
lttng uses the linux monotonic clock from a realtime thread
it might deadlock really good ;)

Norbert
--_000_AM7PR02MB6194C2E06B14077092AA06A0D12A9AM7PR02MB6194eurp_-- --===============7721089565356983973== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev --===============7721089565356983973==--