From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Gleixner <tglx@linutronix.de>
Subject: Re: futex(2) man page update help request
Date: Sat, 24 Jan 2015 11:05:29 +0100 (CET)
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To: Torvald Riegel <triegel@redhat.com>
Cc: Darren Hart <dvhart@linux.intel.com>, "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>, Carlos O'Donell <carlos@redhat.com>, Ingo Molnar <mingo@elte.hu>, Jakub Jelinek <jakub@redhat.com>, "linux-man@vger.kernel.org" <linux-man@vger.kernel.org>, lkml <linux-kernel@vger.kernel.org>, Davidlohr Bueso <davidlohr.bueso@hp.com>, Arnd Bergmann <arnd@arndb.de>, Steven Rostedt <rostedt@goodmis.org>, Peter Zijlstra <peterz@infradead.org>, Linux API <linux-api@vger.kernel.org>, Darren Hart <dvhart@infradead.org>, Anton Blanchard <anton@samba.org>, Petr Baudis <pasky@suse.cz>, Eric Dumazet <edumazet@google.com>, bill o gallmeister <bgallmeister@gmail.com>, Jan Kiszka <jan.kiszka@siemens.com>, Daniel Wagner <wagi@monom.org>, Rich Felker <dalias@libc.org>
List-Id: linux-api@vger.kernel.org

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@gmail.com> 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