From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v2] introduce atomic_pointer to fix a race condition in
 cancelable mcs spinlocks
Date: Mon, 02 Jun 2014 10:38:18 -0700
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Cc: Mikulas Patocka <mpatocka@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>, jejb@parisc-linux.org,
	deller@gmx.de, John David Anglin <dave.anglin@bell.net>,
	linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org,
	paulmck@linux.vnet.ibm.com, chegu_vinod@hp.com, tglx@linutronix.de,
	riel@redhat.com, akpm@linux-foundation.org, davidlohr@hp.com,
	andi@firstfloor.org, aswin@hp.com, scott.norton@hp.com
To: Waiman Long <waiman.long@hp.com>, Jason Low <jason.low2@hp.com>
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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