On Fri, 23 Jan 2015, Torvald Riegel wrote:
> On Fri, 2015-01-16 at 16:46 -0800, Darren Hart wrote:
> > On 1/16/15, 12:54 PM, "Michael Kerrisk (man-pages)"
> > <mtk.manpages@xxxxxxxxx> wrote:
> >
> > >Color me stupid, but I can't see this in futex_requeue(). Where is that
> > >check that is "independent of the requeue type (normal/pi)"?
> > >
> > >When I look through futex_requeue(), all the likely looking sources
> > >of EINVAL are governed by a check on the 'requeue_pi' argument.
> >
> >
> > Right, in the non-PI case, I believe there are valid use cases: move to
> > the back of the FIFO, for example (OK, maybe the only example?).
>
> But we never guarantee a futex is a FIFO, or do we? If we don't, then
> such a requeue could be implemented as a no-op by the kernel, which
> would sort of invalidate the use case.
>
> (And I guess we don't want to guarantee FIFO behavior for futexes.)
The (current) behaviour is:
real-time threads: FIFO per priority level
sched-other threads: FIFO independent of nice level
The wakeup is priority ordered. Highest priority level first.
Thanks,
tglx
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