linux-kernel - Re: [PATCH v9 2/5] qrwlock x86: Enable x86 to use queue read/write lock

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Date:	Tue, 21 Jan 2014 11:00:58 -0500
From:	Waiman Long <waiman.long@...com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	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,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michel Lespinasse <walken@...gle.com>,
	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>, "" <aswin@...com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH v9 2/5] qrwlock x86: Enable x86 to use queue read/write
 lock

On 01/20/2014 11:16 AM, Steven Rostedt wrote:
> On Mon, 20 Jan 2014 17:08:06 +0100
> Peter Zijlstra<peterz@...radead.org>  wrote:
>
>> On Tue, Jan 14, 2014 at 11:44:04PM -0500, Waiman Long wrote:
>>> This patch makes the necessary changes at the x86 architecture specific
>>> layer to enable the presence of the CONFIG_QUEUE_RWLOCK kernel option
>>> to replace the read/write lock by the queue read/write lock.
>>>
>>> It also enables the CONFIG_QUEUE_RWLOCK option by default for x86 which
>>> will force the use of queue read/write lock. That will greatly improve
>>> the fairness of read/write lock and eliminate live-lock situation
>>> where one task may not get the lock for an indefinite period of time.
>>>
>>> Signed-off-by: Waiman Long<Waiman.Long@...com>
>>> Reviewed-by: Paul E. McKenney<paulmck@...ux.vnet.ibm.com>
>>> ---
>>>   arch/x86/Kconfig                      |    1 +
>>>   arch/x86/include/asm/spinlock.h       |    2 ++
>>>   arch/x86/include/asm/spinlock_types.h |    4 ++++
>>>   3 files changed, 7 insertions(+), 0 deletions(-)
>> This patch doesn't have nearly enough -, you should rip out all traces
>> of the old rwlock. There's no point in having it configurable, either
>> qrwlock is good or not.
> Although having something that switches back to the old method gives
> more users the way to compare. Especially to catch any regressions.
>
> Make one release with it configurable, then drop it.
>
> -- Steve

Yes, I agree that it will be more prudent to leave the original rwlock 
implementation there for one or two release cycles before getting rid of 
them entirely.

-Longman
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