Subject: Re: any fairness in NTPL pthread mutexes?
From: Lee Revell <rlrevell@joe-job.com>
To: Christopher Friesen <cfriesen@nortel.com>
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <1130781965.32101.63.camel@mindpipe>
References: <43665B08.6040005@nortel.com>
	 <1130781965.32101.63.camel@mindpipe>
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Date: Mon, 31 Oct 2005 17:09:20 -0500
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On Mon, 2005-10-31 at 13:06 -0500, Lee Revell wrote:
> On Mon, 2005-10-31 at 11:57 -0600, Christopher Friesen wrote:
> > I'm using NPTL.
> > 
> > If I have a pthread mutex currently owned by a task, and two other tasks 
> > try to lock it, when the mutex is unlocked, are there any rules about 
> > the order in which the waiting tasks get the mutex (ie priority, FIFO, 
> > etc.)?
> 
> I believe it's currently FIFO in violation of POSIX which specifies
> priority based wakeup.  AIUI one of the main goals of the realtime &
> robust mutexes work is to fix this.

Sorry this is wrong - the current behavior is allowed by POSIX for
SCHED_OTHER but not SCHED_FIFO or _RR.

Lee

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