linux-kernel - Re: NPTL mutex and the scheduling priority

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Message-Id: <20060907.171158.130239448.nemoto@toshiba-tops.co.jp>
Date:	Thu, 07 Sep 2006 17:11:58 +0900 (JST)
From:	Atsushi Nemoto <anemo@....ocn.ne.jp>
To:	sebastien.dugue@...l.net
Cc:	jakub@...hat.com, arjan@...radead.org, mingo@...hat.com,
	linux-kernel@...r.kernel.org, pierre.peiffer@...l.net
Subject: Re: NPTL mutex and the scheduling priority

On Tue, 13 Jun 2006 01:06:28 +0900 (JST), Atsushi Nemoto <anemo@....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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