linux-kernel - Re: [PATCH v4 1/3] qrwlock: A queue read/write lock implementation

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Message-ID: <52692AE7.3060701@hp.com>
Date:	Thu, 24 Oct 2013 10:12:55 -0400
From:	Waiman Long <waiman.long@...com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	walken@...gle.com, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Rik van Riel <riel@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	George Spelvin <linux@...izon.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH v4 1/3] qrwlock: A queue read/write lock implementation

On 10/24/2013 06:14 AM, Thomas Gleixner wrote:
> On Wed, 23 Oct 2013, Waiman Long wrote:
>> On 10/23/2013 08:00 AM, walken@...gle.com wrote:
>>>> +	/*
>>>> +	 * Wait until the next one in queue set up the next field
>>>> +	 */
>>>> +	while (likely(!(next = ACCESS_ONCE(node->next))))
>>>> +		cpu_relax();
>>>> +	/*
>>>> +	 * The next one in queue is now at the head
>>>> +	 */
>>>> +notify_next:
>>>> +	barrier();
>>>> +	ACCESS_ONCE(next->wait) = false;
>>>> +	smp_wmb();
>>>> +}
>>> I believe this could be unified with mspin_lock() / mspin_unlock() in
>>> kernel/mutex.c ? (there is already talk of extending these functions
>>> to be used by rwsem for adaptive spinning as well...)
>> It probably can, but the unification can wait until the code are in.
> The unification has to be done as a part of this series. Cleanups are
> part of the development process of new code and not an optional
> feature.
>
> Thanks,
>
> 	tglx
>

There is an outstanding rwsem patch series that is doing the 
unification. I am waiting for that patch series to be at least in a tip 
or linux-next branch before doing the unification. Otherwise, it will 
cause merge conflict.

-Longman
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