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

[Erica Bugden]

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 at lists.lttng.org <mailto:lttng-dev at 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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