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

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Date:	Thu, 24 Oct 2013 09:24:49 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Waiman Long <waiman.long@...com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, 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>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH v4 1/3] qrwlock: A queue read/write lock implementation

On Thu, 2013-10-24 at 10:12 -0400, Waiman Long wrote:
> 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.

We can merge the 3 MCS patches of the rwsem patch series first
while we continue to work on other rwsem patches. These 3 
patches are independent of the other rwsem patches.
They separate out the MCS locking into its own file and clean up
the code.

MCS Lock: Restructure the MCS lock defines and locking
https://lkml.org/lkml/2013/10/2/647
MCS Lock: optimizations and extra comments
https://lkml.org/lkml/2013/10/2/644
MCS Lock: Barrier corrections
https://lkml.org/lkml/2013/10/2/650

Thanks.

Tim



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