linux-kernel - Re: [PATCH] WorkStruct: Implement generic UP cmpxchg() where an arch doesn't support it

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Date:	Fri, 8 Dec 2006 16:31:27 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Christoph Lameter <clameter@....com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	David Howells <dhowells@...hat.com>, torvalds@...l.org,
	akpm@...l.org, linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH] WorkStruct: Implement generic UP cmpxchg() where an arch doesn't support it

On Fri, Dec 08, 2006 at 08:06:23AM -0800, Christoph Lameter wrote:
> On Fri, 8 Dec 2006, Russell King wrote:
> 
> > I'm trying to suggest a better implementation for atomic ops rather
> > than just bowing to this x86-centric "cmpxchg is the best, everyone
> > must implement it" mentality.
> 
> cmpxchg is the simplest solution to realize many other atomic operations 
> and its widely available on a wide variety of platforms. It is the most 
> universal atomic instruction that I know of. Other atomic operations may 
> be more efficient but certainly cmpxchg is the most universal.
> 
> Having multiple instructions with restrictions of what can be done in 
> between just complicates the use and seems to be arch specific. I have not 
> seen a better solution. Are you really advocating the weirdly complex 
> ll/sc be adopted by other architectures?

You're advocating cmpxchg is adopted by all architectures.  It isn't
available on many architectures, and those which it can be requires
unnecessarily complicated coding.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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