linux-kernel - Re: [PATCH] s390: more efficient smp barriers

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Message-ID: <20160111090736.63a99647@mschwide>
Date:	Mon, 11 Jan 2016 09:07:36 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Ingo Molnar <mingo@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Davidlohr Bueso <dave@...olabs.net>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	linux-s390@...r.kernel.org
Subject: Re: [PATCH] s390: more efficient smp barriers

On Sun, 10 Jan 2016 13:53:26 +0200
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> As per: lkml.kernel.org/r/20150921112252.3c2937e1@...hwide
> atomics imply a barrier on s390, so s390 should change
> smp_mb__before_atomic and smp_mb__after_atomic to barrier() instead of
> smp_mb() and hence should not use the generic versions.
> 
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Suggested-by: Martin Schwidefsky <schwidefsky@...ibm.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> 
> This is on top of arch barrier cleanup patchset,
> will be included in v3 of that patchset.
> 
>  arch/s390/include/asm/barrier.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
> index 4d26fa4..5c8db3c 100644
> --- a/arch/s390/include/asm/barrier.h
> +++ b/arch/s390/include/asm/barrier.h
> @@ -45,6 +45,9 @@ do {									\
>  	___p1;								\
>  })
> 
> +#define __smp_mb__before_atomic()	barrier()
> +#define __smp_mb__after_atomic()	barrier()
> +
>  #include <asm-generic/barrier.h>
> 
>  #endif /* __ASM_BARRIER_H */

Feel free to add:
Acked-by: Martin Schwidefsky <schwidefsky@...ibm.com>

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.