linux-kernel - Re: [PATCH 6/24] make atomic_read() behave consistently on frv

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Message-ID: <46BB46B2.60808@redhat.com>
Date:	Thu, 09 Aug 2007 12:54:10 -0400
From:	Chris Snook <csnook@...hat.com>
To:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	torvalds@...ux-foundation.org
CC:	netdev@...r.kernel.org, akpm@...ux-foundation.org, ak@...e.de,
	heiko.carstens@...ibm.com, davem@...emloft.net,
	schwidefsky@...ibm.com, wensong@...ux-vs.org, horms@...ge.net.au,
	wjiang@...ilience.com, cfriesen@...tel.com, zlynx@....org,
	rpjday@...dspring.com, jesper.juhl@...il.com
Subject: Re: [PATCH 6/24] make atomic_read() behave consistently on frv

Chris Snook wrote:
> From: Chris Snook <csnook@...hat.com>
> 
> Make atomic_read() volatile on frv.  This ensures that busy-waiting
> for an interrupt handler to change an atomic_t won't get compiled to an
> infinite loop, consistent with SMP architectures.

To head off the criticism, I admit this is an oversimplification, and true 
busy-waiters should be using cpu_relax(), which contains a barrier.  As 
discussed in recent threads, there are other cases which can be optimized by 
removing the need for a barrier, and having behavior consistent with 
architectures where the benefit is more profound is also valuable.

	-- Chris
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