Re: [LTP] [PATCH v2] sched_football: synchronize with kickoff flag to reduce skew

[Cyril Hrubis <chrubis@suse.cz>]

Hi!
> > > >  static void do_setup(void)
> > > >  {
> > > > +   if (!tst_check_preempt_rt())
> > > > +           tst_brk(TCONF, "Test requires real-time kernel");
> > >
> > > I understood Cyril is really suggesting to keep it [1]. I would also
> > vote to
> > > keep it (we still have some time to see if it got fixed before release).
> > >
> > > I know we had this discussion in the past (some of your colleague
> > suggesting it
> > > should not be run on non-RT kernel), so I'm not pushing for it.
> >
> > I stil do not understand reasons for disabling the test. The POSIX
> > realtime schedulling classes have to work properly regardless of the
> > kernel flavor. Why should we turn the test off on non-rt kernel then?
> >
> 
> No special reasons. I still can sporadically catch the failure on non-RT
> kernel with even sleep 2 seconds.

That is very strange. The SCHED_FIFO threads should preempty any lower
prio thread as long as they become runable and should stay running until
they finish or yield. Two seconds should be more than enough for that to
happen.

> Thus, I took this very extreme approach, because on non-RT kernel, sleep
> may not have a particularly perfect effect, I guess the stock kernel with
> sched_setscheduler(, SCHED_FIFO, ) is still has scheduling skew with
> workload.

Does this happen on vanilla Linux as well or only on RedHat kernels?

Because AFAIK the test started to fail on SUSE only after the change
that introduced barriers.

-- 
Cyril Hrubis
chrubis@suse.cz

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