linux-kernel - Re: [PATCH v4 0/3] qspinlock: Introducing a 4-byte queue spinlock

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Message-ID: <5303B4C4.2040907@hp.com>
Date:	Tue, 18 Feb 2014 14:30:12 -0500
From:	Waiman Long <waiman.long@...com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.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>,
	Daniel J Blueman <daniel@...ascale.com>,
	Alexander Fyodorov <halcy@...dex.ru>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>,
	Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@...com>
Subject: Re: [PATCH v4 0/3] qspinlock: Introducing a 4-byte queue spinlock

On 02/18/2014 02:31 AM, Peter Zijlstra wrote:
> On Mon, Feb 17, 2014 at 02:47:03PM -0800, H. Peter Anvin wrote:
>> On 02/17/2014 12:41 PM, Waiman Long wrote:
>>> v3->v4:
>>>   - Remove debugging code and fix a configuration error
>>>   - Simplify the qspinlock structure and streamline the code to make it
>>>     perform a bit better
>>>   - Add an x86 version of asm/qspinlock.h for holding x86 specific
>>>     optimization.
>>>   - Add an optimized x86 code path for 2 contending tasks to improve
>>>     low contention performance.
>>>
>>> v2->v3:
>>>   - Simplify the code by using numerous mode only without an unfair option.
>>>   - Use the latest smp_load_acquire()/smp_store_release() barriers.
>>>   - Move the queue spinlock code to kernel/locking.
>>>   - Make the use of queue spinlock the default for x86-64 without user
>>>     configuration.
>>>   - Additional performance tuning.
>>>
>>> v1->v2:
>>>   - Add some more comments to document what the code does.
>>>   - Add a numerous CPU mode to support>= 16K CPUs
>>>   - Add a configuration option to allow lock stealing which can further
>>>     improve performance in many cases.
>>>   - Enable wakeup of queue head CPU at unlock time for non-numerous
>>>     CPU mode.
>>>
>>> This patch set introduces a queue-based spinlock implementation that
>>> can replace the default ticket spinlock without increasing the size
>>> of the spinlock data structure. As a result, critical kernel data
>>> structures that embed spinlock won't increase in size and breaking
>>> data alignments.
>>>
>> This is starting to look good, so I have pulled it into
>> tip:x86/spinlocks to start give it some testing mileage.
> It very much needs paravirt muck before we can even consider it.

I will start looking at how to make it work with paravirt. Hopefully, it 
won't take too long.

-Longman
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