linux-kernel - Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

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Message-ID: <alpine.DEB.1.10.0901081440410.24688@gandalf.stny.rr.com>
Date:	Thu, 8 Jan 2009 14:45:29 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Chris Mason <chris.mason@...cle.com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, paulmck@...ux.vnet.ibm.com,
	Gregory Haskins <ghaskins@...ell.com>,
	Matthew Wilcox <matthew@....cx>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>,
	Peter Morreale <pmorreale@...ell.com>,
	Sven Dietrich <SDietrich@...ell.com>
Subject: Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning


On Thu, 8 Jan 2009, Chris Mason wrote:
> On Thu, 2009-01-08 at 13:14 -0500, Steven Rostedt wrote:
> > 
> > If it was the current process that preempted the owner and these are RT 
> > tasks pinned to the same CPU and the owner is of lower priority than the 
> > spinner, we have a deadlock!
> > 
> > Hmm, I do not think the need_sched here will even fix that :-/
> 
> RT tasks could go directly to sleeping.  The spinner would see them on
> the list and break out.

True, we could do:

	if (owner) {
		if (!spin_on_owner(lock, owner))	
			break;
	} else if (rt_task(current))
		break;

That would at least solve the issue in the short term.

-- Steve
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