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 23:13:12 -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:

> +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;
> +}


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