linux-kernel - Re: [PATCH v2] introduce atomic_pointer to fix a race condition in cancelable mcs spinlocks

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Date:	Mon, 02 Jun 2014 10:38:18 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Waiman Long <waiman.long@...com>, Jason Low <jason.low2@...com>
CC:	Mikulas Patocka <mpatocka@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>, jejb@...isc-linux.org,
	deller@....de, John David Anglin <dave.anglin@...l.net>,
	linux-parisc@...r.kernel.org, linux-kernel@...r.kernel.org,
	paulmck@...ux.vnet.ibm.com, chegu_vinod@...com, tglx@...utronix.de,
	riel@...hat.com, akpm@...ux-foundation.org, davidlohr@...com,
	andi@...stfloor.org, aswin@...com, scott.norton@...com
Subject: Re: [PATCH v2] introduce atomic_pointer to fix a race condition in
 cancelable mcs spinlocks

On 06/02/2014 10:25 AM, Waiman Long wrote:
> 
> Doing an xchg is a very expensive operation compared with ACCESS_ONCE. I
> will not suggest doing that to make it right for PA-RISC at the expense
> of performance in other architectures.
> 

And of course, this gets into the toxic question: what are reasonable
minimum requirements for Linux?  How far do we need to stretch to
support niche architectures which have very small (Linux) userbases?

	-hpa


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