linux-kernel - Re: [RFC][PATCH v2 5/5] mutex: Give spinners a chance to spin_on_owner if need

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Date:	Mon, 03 Feb 2014 12:55:34 -0800
From:	Jason Low <jason.low2@...com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <Waiman.Long@...com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Davidlohr Bueso <davidlohr@...com>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>, chegu_vinod@...com
Subject: Re: [RFC][PATCH v2 5/5] mutex: Give spinners a chance to
 spin_on_owner if need_resched() triggered while queued

On Mon, 2014-02-03 at 20:25 +0100, Peter Zijlstra wrote:
> On Mon, Feb 03, 2014 at 10:39:20AM -0800, Jason Low wrote:
> > > To avoid the xchg on every loop.
> > 
> > Ah yes, we want to use xchg() on &node->next.
> > 
> > Since the cmpxchg() is now in a loop in the unlock function, an
> > additional (*lock == node) check before the cmpxchg() would also be nice
> > to avoid spinning on cmpxchg() there too.
> 
> Right, I have the below; you can find the patches this depends upon
> here:
> 
>   http://programming.kicks-ass.net/sekrit/patches.tar.bz2
> 
> ---
> Subject: locking, mutex: Cancelable MCS lock for adaptive spinning
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Wed, 29 Jan 2014 12:51:42 +0100
> 
> Since we want a task waiting for a mutex_lock() to go to sleep and
> reschedule on need_resched() we must be able to abort the
> mcs_spin_lock() around the adaptive spin.
> 
> Therefore implement a cancelable mcs lock.
> 
> XXX: anybody got a better name than m_spinlock?

So I was thinking something along the lines of
mcs_spin_lock_cancelable() as that's essentially what this function
does.

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