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Date: Thu, 30 Jan 2014 20:35:39 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <Waiman.Long@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Arnd Bergmann <arnd@arndb.de>,
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        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
Message-ID: <20140130193539.GL5002@laptop.programming.kicks-ass.net>
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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 :-)