linux-kernel - Re: [PATCH v4 3/3] qspinlock, x86: Add x86 specific optimization for 2 contending tasks

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Date:	Fri, 21 Feb 2014 18:26:33 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Waiman Long <waiman.long@...com>
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 v4 3/3] qspinlock, x86: Add x86 specific optimization for
 2 contending tasks

On Fri, Feb 21, 2014 at 12:09:57PM -0500, Waiman Long wrote:
> On 02/21/2014 12:08 PM, Waiman Long wrote:
> >On 02/21/2014 07:12 AM, Peter Zijlstra wrote:
> >>
> >>Why is this x86 only code?
> >
> >The code is making use of the fact that byte write is atomic which is true
> >in x86 and probably in a few other architectures. I could pull these codes
> >into the generic qspinlock.c file and set a flag in the asm header file to
> >activate it if it is what you want.
> >
> >-Longman
> 
> BTW, I also assume that 8-bit and 16-bit cmpxchg() and xchg() are available.

Right, screw Alpha :-) Just pull it into the generic code; its far too
much code to replicate per arch.
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