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

[Petr Vorel <pvorel@suse.cz>]

Hi Alessandro,

> Hello Petr,
...
> > LGTM. Could you please test if starvation.c worked previously?
> > Or was it always broken?

> Before submitting the patch, I tested the case in various environments.
> One thing that puzzled me for a while was the test's high sensitivity to
> latencies.
> While it works correctly on bare-metal systems under the intended
> conditions with the CFS scheduler, running it on a real-time kernel
> or in a virtualized/emulated environment is likely to cause the
> test to fail.

> This patch addresses the real-time kernel scenario, which is relatively
> easier to handle.
> In a separate RFC patch I plan to send, I would like to ask the
> community for guidance on how to handle the virtualization/emulation
> environment issue.

Thanks, reply send.

FYI there is a git freeze before upcoming release, only fixes are merged.
https://lore.kernel.org/ltp/5202b2ba-a13e-4250-97c5-937dde849975@suse.com/T/#t

But fixes like this should go in (I'll leave the decision to Cyril).

> > Reviewed-by: Petr Vorel <pvorel@suse.cz>

> > > +int tst_check_preempt_rt(void)
> > > +{
> > > +     struct utsname uval;
> > > +
> > > +     uname(&uval);
> > > +     if (strstr(uval.version, "PREEMPT_RT"))
> > > +             return -1;
> > > +     return 0;
> > > +}
> > > diff --git a/testcases/kernel/sched/cfs-scheduler/starvation.c b/testcases/kernel/sched/cfs-scheduler/starvation.c
> > > index 901556a7b..c620c9c3e 100644
> > > --- a/testcases/kernel/sched/cfs-scheduler/starvation.c
> > > +++ b/testcases/kernel/sched/cfs-scheduler/starvation.c
> > > @@ -82,6 +82,9 @@ static void setup(void)

> > >       CPU_ZERO(&mask);

> > > +     if (tst_check_preempt_rt())
> > > +             tst_brk(TCONF, "This test is not designed for the RT kernel");
> > nit: I would move it above CPU_ZERO().
> Ok, I'll fix it in the v2

Thanks!

> > NOTE: we should also move tst_has_slow_kconfig() check to be at the top of
> > setup(). But that's unrelated. Also at least on Tumbleweed and SLES which get
> > detected as slow due CONFIG_LATENCYTOP test was worked before.

> Want me to address this issue?

Already done:
https://patchwork.ozlabs.org/project/ltp/patch/20250120143420.815363-1-pvorel@suse.cz/

Kind regards,
Petr

> > Kind regards,
> > Petr


> Cheers
> Alessandro

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