LTTng sched_switch documentation patch.

Chris Johns chrisj at
Tue Aug 27 00:43:24 UTC 2019

On 26/8/19 8:16 pm, Ravindra Kumar Meena wrote:
> Hello Chris and Sebastian,
> I have attached the updated LTTng sched_switch documentation patch(v4). This one
> is a whole single patch.
> *What changed v3 to v4:*
> Sebastian's patch for rtems-libbsd patch got merged today, So I have removed my
> GitHub repo link from the documentation and updated it. There are some minor
> changes like whitespace fixes etc.
> Please review the patch.

Steps [1-5] ... Why not use the REST list numbering rather than inventing
something? This is for 10.5.1 Trace Compass and 10.5.2.

10.5.1 Trace Compass

Step 1:

This is specific to QEMU and that leaves me wondering if this method of trace
works on all targets.

The language is not specific. For example "The host can be connected to target
via telnet." for what purpose and why? The documentation does not provide me
with any direction.

10.5.2 RTEMS LTTng Trace Generation Example

Step 1:

I think the language is too casual, for example ...

"Step 1: Clone the repositories rtems-libbsd and rtems-tools and set up the
environment, if haven’t done already."

This should reference the specific sections in the User manual that detail how
to do this.

Step 3:

Can the `Host` box be expanded to show how each of the other parts are connected?

Step 2:

I feel we should reference the rtems-run command to run these qemu sessions. If
there needs to be extra detail that handles the net connection then this should
be investigated and added to `rtems-run`.

Step 3:

This does not specify the host these command are to be used on. If this is Linux
are these command available on all distros? It is complicated to make a
cross-platform way to handle this but this is what needs to be solved for RTEMS.
I am not sure what is needed but I suspect we may need a tool in rtems-tools to
wrap the cross-platform ways of doing this.

Telnet is not available on MacOS any more. This has been discussed on this list
before. The issue is the User Manual is for all hosts and we need to consider
and cater for a new user who uses MacOS. There is no indication of why this is
needed to use this method of trace.

The reason I raise these things is a core developer would need to clean this up.

Step 4:

I raised using commands in the build before now. Please do not do this. A user
will not built the rtems-tool repo by hand and will not have a `build`
directory. The RSB will build and install the tools.

What is `raw-data`? There is no explanation of the types of data, where they
come from and what uses them.

Step 5:

Maybe it would be good to present more detail on what is needed to install Trace
Compass. This could be in the Trace Compass section. Has anyone promoting this
method of trace actually tried FreeBSD and solved how this is done? I hope this
is not being left to a FreeBSD user to sort out.

I followed the link and see MacOS, Linux, and Windows. Also I think the Add-On
link is too specific and maybe fragile. An RTEMS release will capture this link
and it needs to be around for a number of years.

Step 6:

I see no value in the screen capture. It is impossible to see any detail and
there is no context explaining any parts of interest. I can see what the tool
does on the Trace Compass website.

"Move the trace and metadata generated in common folder ..." ? What is this?


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