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Date: Wed, 6 Nov 2013 13:59:14 -0800
Message-ID: <CANN689FY67Nu0irKyPxsEPK3NzbpgzKQyW5wLkESfPib9_-zHw@mail.gmail.com>
Subject: Re: [PATCH v3 0/4] MCS Lock: MCS lock code cleanup and optimizations
From: Michel Lespinasse <walken@google.com>
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To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>, Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>, Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>, linux-arch@vger.kernel.org, Linus Torvalds <torvalds@linux-foundation.org>, Waiman Long <waiman.long@hp.com>, Andrea Arcangeli <aarcange@redhat.com>, Alex Shi <alex.shi@linaro.org>, Andi Kleen <andi@firstfloor.org>, Davidlohr Bueso <davidlohr.bueso@hp.com>, Matthew R Wilcox <matthew.r.wilcox@intel.com>, Dave Hansen <dave.hansen@intel.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Rik van Riel <riel@redhat.com>, Peter Hurley <peter@hurleysoftware.com>, "Paul E.McKenney" <paulmck@linux.vnet.ibm.com>, Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>, George Spelvin <linux@horizon.com>, Arnd Bergmann <arnd@arndb.de>, Aswin Chandramouleeswaran <aswin@hp.com>, Scott J Norton <scott.norton@hp.com>, Will Deacon <will.deacon@arm.com>, "Figo.zhang" <figo1802@gmail.com>

On Wed, Nov 6, 2013 at 1:42 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> Perhaps I'm missing something here, but what is MCS lock and what is the
> value?

Its a kind of queued lock where each waiter spins on a a separate
memory word, instead of having them all spin on the lock's memory
word. This helps with scalability when many waiters queue on the same
lock.

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.

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