[LTP] [PATCH v3] cfs-scheduler/starvation.c: Skip test on realtime kernels

[Alessandro Carminati]

Hi Petr,

Thanks for the feedback.

On Mon, Jan 27, 2025 at 10:39 AM Petr Vorel <pvorel@suse.cz> wrote:
>
> > This commit introduces a check in the starvation test case to detect and
> > skip execution on realtime kernels. The test is designed for use with the
> > Completely Fair Scheduler and produces meaningless results when run on
> > realtime kernels.
>
> > By skipping the test on realtime kernels, we avoid confusion caused by
> > misleading results.
>
> Thanks a lot for fixing -1 in v3. I was thinking to merge v2 and fix -1
> manually, but I'm really not sure if the test is meaningless for realtime.
> Was the test really written for CFS? It would be nice to get ack from any
> realtime developer.
>
> BTW test is working well on x86_64 SLES realtime kernel on VM, i.e. both you
> want to skip (RT) or warn about unreliable results (VM). That of course
> does not mean it's relevant for RT kernel.

Here's what I observed:
* In our CI pipeline, the test consistently fails on our RT kernel running
  on AARCH64 boards.
* Upon investigating and reading through the code, I noticed that the test
  seems to rely on an equal number of times the child and parent tasks get
  scheduled. This behavior aligns with how CFS works... less with RT.
* That said, there are scenarios where CFS and RT might make similar
  scheduling decisions, particularly in RT when all tasks share the same
  priority.
* Finally, as a hint, I noticed that the test is currently placed in the
  cfs-scheduler directory. I interpret this as a strong suggestion from the
  author that the test was intended for the CFS scheduler.

>
> Kind regards,
> Petr
>


-- 
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Thanks
Alessandro
172