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SubjectRe: NPTL mutex and the scheduling priority
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On Tue, 13 Jun 2006 01:06:28 +0900 (JST), Atsushi Nemoto <anemo@mba.ocn.ne.jp> wrote:
> > > Really FUTEX_WAKE/FUTEX_REQUEUE can't use a FIFO. I think there was a patch
> > > floating around to use a plist there instead, which is one possibility,
> > > another one is to keep the queue sorted by priority (and adjust whenever
> > > priority changes - one thread can be waiting on at most one futex at a
> > > time).
> > >
> >
> > The patch you refer to is at
> > http://marc.theaimsgroup.com/?l=linux-kernel&m=114725326712391&w=2
>
> Thank you all. I'll look into PI futexes which seems the right
> direction, but I still welcome short term (limited) solutions,
> hopefully work with existing glibc. I'll look at the plist patch.

Three months after, I have tried kernel 2.6.18 with recent glibc. I
got desired results for pthread_mutex_unlock and
pthread_cond_broadcast, with PI-mutex.

But pthread_cond_signal and sem_post still wakeup a thread in FIFO
order, as you can guess.

With the plist patch (applied by hand), I can get desired behavior.
Thank you. But It seems the patch lacks reordering on priority
changes.

Are there any patch or future plan to address remaining wakeup-order
issues?


<off_topic>
BTW, If I tried to create a PI mutex on a kernel without PI futex
support, pthread_mutexattr_setprotocol(PTHREAD_PRIO_INHERIT) returned
0 and pthread_mutex_init() returned ENOTSUP. This is not a right
behavior according to the manual ...
</off_topic>

---
Atsushi Nemoto
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