linux-kernel - Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

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Message-ID: <18115.48863.331246.638826@cargo.ozlabs.ibm.com>
Date:	Thu, 16 Aug 2007 13:05:03 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Satyam Sharma <satyam@...radead.org>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	Christoph Lameter <clameter@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Chris Snook <csnook@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arch@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	netdev@...r.kernel.org, Andrew Morton <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,
	segher@...nel.crashing.org
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all
 architectures

Satyam Sharma writes:

> I can't speak for this particular case, but there could be similar code
> examples elsewhere, where we do the atomic ops on an atomic_t object
> inside a higher-level locking scheme that would take care of the kind of
> problem you're referring to here. It would be useful for such or similar
> code if the compiler kept the value of that atomic object in a register.

If there is a higher-level locking scheme then there is no point to
using atomic_t variables.  Atomic_t is specifically for the situation
where multiple CPUs are updating a variable without locking.

Paul.
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