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

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Message-ID: <52F2FD2A.1020704@hp.com>
Date:	Wed, 05 Feb 2014 22:10:34 -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 02/03/2014 06:40 AM, Peter Zijlstra wrote:
> On Fri, Jan 31, 2014 at 02:24:33PM -0500, Waiman Long wrote:
>> Light contention is the only case where the qspinlock may not perform as
>> good as the ticket spinlock. I know this is the most common case. However, I
>> would argue that the slowdown, if any, will not be really noticeable. This
>> is what I will try to find out.
> Please also explain why things are slower/faster. Thomas tried to get
> you to do so a few months back, but you kept deflecting.

It is not easy to have a test case to test light contention. I am trying 
to create custom test case to get that data.

-Longman
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