linux-kernel - Re: [PATCH 2/2]: atomic_t: Remove volatile from atomic

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Message-ID: <20100519225046.GO2237@linux.vnet.ibm.com>
Date:	Wed, 19 May 2010 15:50:46 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	David Miller <davem@...emloft.net>
Cc:	npiggin@...e.de, torvalds@...ux-foundation.org, anton@...ba.org,
	akpm@...ux-foundation.org, willy@...ux.intel.com,
	benh@...nel.crashing.org, paulus@...ba.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2]: atomic_t: Remove volatile from atomic_t definition

On Wed, May 19, 2010 at 12:54:49PM -0700, David Miller wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> Date: Wed, 19 May 2010 08:01:32 -0700
> 
> > On Wed, May 19, 2010 at 11:03:27PM +1000, Nick Piggin wrote:
> >> For atomic_read it shouldn't matter unless gcc is *really* bad at it.
> >> Ah, for atomic_read, the required semantic is surely ACCESS_ONCE, so
> >> that's where the volatile is needed? (maybe it would be clearer to
> >> explicitly use ACCESS_ONCE?)
> > 
> > Explicit use of ACCESS_ONCE() where needed makes a lot of sense to me,
> > and allows better code to be generated for initialization and cleanup
> > code where no other task has access to the atomic_t.
> 
> I agree and I want to see this too, but I think with the tree the size
> that it is we have to work backwards at this point.
> 
> Existing behavior by default, and optimized cases get tagged by using
> a new interface (atomic_read_light(), test_bit{,s}_light(), etc.)

Fair enough!

							Thanx, Paul
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