linux-kernel - Re: [RFC][PATCH 3/5] arch: s/smp_mb__(before|after)_(atomic|clear)_(dec,inc,bit)/smp_mb_

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Message-ID: <20140207095241.GA5976@mudshark.cambridge.arm.com>
Date:	Fri, 7 Feb 2014 09:52:41 +0000
From:	Will Deacon <will.deacon@....com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...nel.org" <mingo@...nel.org>
Subject: Re: [RFC][PATCH 3/5] arch:
 s/smp_mb__(before|after)_(atomic|clear)_(dec,inc,bit)/smp_mb__\1/g

On Thu, Feb 06, 2014 at 07:12:04PM +0000, Paul E. McKenney wrote:
> On Thu, Feb 06, 2014 at 02:48:28PM +0100, Peter Zijlstra wrote:
> > Because atomic ops are implemented the same across an architecture,
> > the current incomplete set of extra barriers:
> >
> >   smp_mb__before_atomic_inc()
> >   smp_mb__after_atomic_inc()
> >   smp_mb__before_atomic_dec()
> >   smp_mb__after_atomic_dec()
> >   smp_mb__before_clear_bit()
> >   smp_mb__after_clear_bit()
> >
> > is both incomplete and superfluous.
> >
> > It is incomplete because there are far more atomic operations that do
> > not return values -- such as atomic_add(), set_bit() etc. And it is
> > superfluous because they're all the same anyway.
> >
> > Simplify things by reducing the triplicate set into a single set of
> > barriers that is valid for all void atomic ops:
> >
> >   smp_mb__before_atomic()
> >   smp_mb__after_atomic()
> >
> > Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> 
> I very much like the API shrinkage.  The RCU changes are good, and
> I believe that the rest is OK too, though my eyes were going a bit
> buggy towards the end...
> 
> Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

... and the arm[64] parts look fine to me.

  Acked-by: Will Deacon <will.deacon@....com>

Usual comment about upcoming conflicts :)

Will
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