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Message-ID: <1391497992.2774.17.camel@j-VirtualBox>
Subject: Re: [RFC][PATCH v2 5/5] mutex: Give spinners a chance to
 spin_on_owner if need_resched() triggered while queued
From: Jason Low <jason.low2@hp.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>, Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Waiman Long <Waiman.Long@hp.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Rik van Riel <riel@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Davidlohr Bueso <davidlohr@hp.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Andi Kleen <andi@firstfloor.org>,
        "Chandramouleeswaran, Aswin" <aswin@hp.com>,
        "Norton, Scott J" <scott.norton@hp.com>, chegu_vinod@hp.com
Date: Mon, 03 Feb 2014 23:13:12 -0800
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On Mon, 2014-02-03 at 20:25 +0100, Peter Zijlstra wrote:

> +void m_spin_unlock(struct m_spinlock **lock)
> +{
> +	struct m_spinlock *node = this_cpu_ptr(&m_node);
> +	struct m_spinlock *next;
> +
> +	if (likely(cmpxchg(lock, node, NULL) == node))
> +		return;

At this current point, (node->next != NULL) is a likely scenario.
Perhaps we can also add the following code here:

	next = xchg(&node->next, NULL);
	if (next) {
		ACCESS_ONCE(next->locked) = 1;
		return;
	}

> +	next = m_spin_wait_next(lock, node, NULL);
> +	if (next)
> +		ACCESS_ONCE(next->locked) = 1;
> +}