linux-kernel - Re: [PATCH v6 3/5] qrwlock: Enable fair queue read/write lock

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Message-ID: <CA+55aFyH_BUrrzft-1JGZ5zL=KxGrUESBBOZnzT=nQm6Ld0V+Q@mail.gmail.com>
Date:	Mon, 18 Nov 2013 10:38:13 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Waiman Long <Waiman.Long@...com>,
	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" <linux-arch@...r.kernel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	George Spelvin <linux@...izon.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH v6 3/5] qrwlock: Enable fair queue read/write lock

On Mon, Nov 18, 2013 at 10:34 AM, Andi Kleen <andi@...stfloor.org> wrote:
>
> FWIW unfair can be faster in some cases. It depends on the workload.

Sure. And we've never cared before.

When we switched over to the ticket spinlocks, we actually had
*numbers* about how the old unfair spinlocks could be faster. And we
still didn't leave a "unfair spinlocks" option. Because it didn't make
sense.

Why would it make sense here?

                Linus
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