linux-kernel - Re: [PATCH v3 1/2] qspinlock: Introducing a 4-byte queue spinlock implementation

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Message-ID: <52EBEB36.9090102@hp.com>
Date:	Fri, 31 Jan 2014 13:28:06 -0500
From:	Waiman Long <waiman.long@...com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	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, 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 v3 1/2] qspinlock: Introducing a 4-byte queue spinlock
 implementation

On 01/30/2014 02:35 PM, Peter Zijlstra wrote:
> On Tue, Jan 28, 2014 at 01:19:10PM -0500, Waiman Long wrote:
>> This patch introduces a new queue spinlock implementation that can
>> serve as an alternative to the default ticket spinlock. Compared with
>> the ticket spinlock, this queue spinlock should be almost as fair as
>> the ticket spinlock. It has about the same speed in single-thread and
>> it can be much faster in high contention situations. Only in light to
>> moderate contention where the average queue depth is around 1-2 will
>> this queue spinlock be potentially a bit slower due to the higher
>> slowpath overhead.
> But light to moderate contention should be the most common case. If your
> spinlock is very heavily contended, it should be broken up.
>
> I would really like more performance numbers for this on single and dual
> socket machines and 'normal' workloads (ha! as if those exist), ie.
> kbuild is all very important to us :-)

Yes, I am planning to get more performance data on low end machines. The 
v3 patch was sent out to spur discussion on this topic while I am trying 
to get more data.

-Longman
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