Message-ID: <52DE99BA.1090204@hp.com>
Date: Tue, 21 Jan 2014 11:00:58 -0500
From: Waiman Long <waiman.long@hp.com>
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To: Steven Rostedt <rostedt@goodmis.org>
CC: Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Arnd Bergmann <arnd@arndb.de>,
        linux-arch@vger.kernel.org, x86@kernel.org,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Michel Lespinasse <walken@google.com>,
        Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        George Spelvin <linux@horizon.com>,
        Tim Chen <tim.c.chen@linux.intel.com>, "" <aswin@hp.com>,
        Scott J Norton <scott.norton@hp.com>
Subject: Re: [PATCH v9 2/5] qrwlock x86: Enable x86 to use queue read/write
 lock
References: <1389761047-47566-1-git-send-email-Waiman.Long@hp.com> <1389761047-47566-3-git-send-email-Waiman.Long@hp.com> <20140120160806.GI30183@twins.programming.kicks-ass.net> <20140120111630.7ceb0aa5@gandalf.local.home>
In-Reply-To: <20140120111630.7ceb0aa5@gandalf.local.home>
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Sender: linux-kernel-owner@vger.kernel.org

On 01/20/2014 11:16 AM, Steven Rostedt wrote:
> On Mon, 20 Jan 2014 17:08:06 +0100
> Peter Zijlstra<peterz@infradead.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@hp.com>
>>> Reviewed-by: Paul E. McKenney<paulmck@linux.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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