Message-ID: <52F2FD2A.1020704@hp.com>
Date: Wed, 05 Feb 2014 22:10:34 -0500
From: Waiman Long <waiman.long@hp.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: 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, Steven Rostedt <rostedt@goodmis.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>,
        Daniel J Blueman <daniel@numascale.com>,
        Alexander Fyodorov <halcy@yandex.ru>,
        Aswin Chandramouleeswaran <aswin@hp.com>,
        Scott J Norton <scott.norton@hp.com>,
        Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@hp.com>
Subject: Re: [PATCH v3 1/2] qspinlock: Introducing a 4-byte queue spinlock
 implementation
References: <1390933151-1797-1-git-send-email-Waiman.Long@hp.com> <1390933151-1797-2-git-send-email-Waiman.Long@hp.com> <20140131150832.GG4941@twins.programming.kicks-ass.net> <52EBF871.5020603@hp.com> <20140203114054.GH8874@twins.programming.kicks-ass.net>
In-Reply-To: <20140203114054.GH8874@twins.programming.kicks-ass.net>
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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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