linux-kernel - Re: [PATCH v3] rwsem: Support optimistic spinning

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Date:	Thu, 01 May 2014 09:39:16 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Davidlohr Bueso <davidlohr@...com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Alex Shi <alex.shi@...aro.org>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E.McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jason Low <jason.low2@...com>,
	Aswin Chandramouleeswaran <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] rwsem: Support optimistic spinning

On Wed, 2014-04-30 at 20:21 -0700, Davidlohr Bueso wrote:

> +
> +static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
> +{
> +	struct task_struct *owner;
> +	bool on_cpu = true;
> +
> +	if (need_resched())
> +		return 0;
> +
> +	rcu_read_lock();
> +	owner = ACCESS_ONCE(sem->owner);
> +	if (owner)
> +		on_cpu = owner->on_cpu;
> +	rcu_read_unlock();
> +
> +	/*
> +	 * If lock->owner is not set, the mutex owner may have
> +	 * just acquired it and not set the owner yet or the mutex

Nitpick. Change the above 2 mutex in comment to rwsem.

> +	 * has been released.
> +	 */
> +	return on_cpu;
> +}
> +

Tim


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