Re: [lttng-dev] Lttng: display active threads in multiple cores.

[Zvi Vered via lttng-dev <lttng-dev@lists.lttng.org>]

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Hi Erica,

Thank you very much for your answer.
Can you please tell what is the added value of ftrace (compared to using
only lttng) ?

Best regards,
Zvika


On Tue, Apr 2, 2024 at 5:11 PM Erica Bugden <ebugden@efficios.com> wrote:

> Hello Zvika,
>
> On 2024-03-29 01:09, Zvi Vered via lttng-dev wrote:
> > Hi Christopher,
> >
> > Thank you very much for your reply.
> > Can you please explain what do you mean by ftrace-enabled kernel ?
>
> I believe what Christopher means by "ftrace-enabled" kernel is that the
> Linux kernel has been configured to include ftrace. Both the ftrace
> tracer and the LTTng tracer use the same kernel tracepoints to extract
> execution information and these tracepoints are included in the kernel
> if ftrace is included.
>
> Most Linux distributions will include ftrace by default. However, you
> can check whether this is the case by searching for `tracefs` in
> `/proc/filesystems` (assuming it's already mounted) or by trying to
> mount `tracefs`. `tracefs` is the filesystem ftrace uses to communicate
> with users.
>
> More details about how to check if ftrace is enabled and how to enable
> it if not:
> https://wiki.linuxfoundation.org/realtime/documentation/howto/tools/ftrace
>
> The "More Information" section points to the primary sources (Linux
> kernel documentation), but I find this page to be a good starting point.
>
> Best,
> Erica
>
> >
> > Best regards,
> > Zvika
> >
> > On Wed, Mar 27, 2024 at 7:32 PM Christopher Harvey via lttng-dev
> > <lttng-dev@lists.lttng.org <mailto:lttng-dev@lists.lttng.org>> wrote:
> >
> >     you can use an ftrace-enabled kernel with lttng (maybe even just
> >     tracecompass) or perfetto to get that kind of trace
> >
> >
> https://archive.eclipse.org/tracecompass.incubator/doc/org.eclipse.tracecompass.incubator.ftrace.doc.user/User-Guide.html
> <
> https://archive.eclipse.org/tracecompass.incubator/doc/org.eclipse.tracecompass.incubator.ftrace.doc.user/User-Guide.html
> >
> >
> >     or
> >
> >     https://ui.perfetto.dev/ <https://ui.perfetto.dev/>
> >
> >     On Wed, Mar 27, 2024, at 5:26 AM, Zvi Vered via lttng-dev wrote:
> >      > Hello,
> >      >
> >      > I have an application with 4 threads.
> >      > I'm required to display on the graph when thread starts working
> >     till it
> >      > blocks for the next semaphore.
> >      >
> >      > But without using the lttng userspace library.
> >      >
> >      > Is it possible ?
> >      >
> >      > Thank you,
> >      > Zvika
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> >
> >
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