From: Martin Schwidefsky <schwidefsky@de.ibm.com>
To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org,
torvalds@linux-foundation.org, will.deacon@arm.com,
peterz@infradead.org, schwidefsky@de.ibm.com,
paulmck@linux.vnet.ibm.com, gang.chen@asianux.com,
heiko.carstens@de.ibm.com, tglx@linutronix.de
Cc: tipbot@zytor.com, linux-tip-commits@vger.kernel.org
Subject: Re: [tip:locking/core] arch,s390: Convert smp_mb__*()
Date: Wed, 23 Apr 2014 09:37:57 +0200 [thread overview]
Message-ID: <20140423093757.2c07c209@mschwide> (raw)
In-Reply-To: <tip-kme5dz5hcobpnufnnkh1ech2@git.kernel.org>
Hi Peter,
On Fri, 18 Apr 2014 06:11:38 -0700
tip-bot for Peter Zijlstra <tipbot@zytor.com> wrote:
> arch,s390: Convert smp_mb__*()
>
> As per the existing implementation; implement the new one using
> smp_mb().
>
> AFAICT the s390 compare-and-swap does imply a barrier, however there
> are some immediate ops that seem to be singly-copy atomic and do not
> imply a barrier. One such is the "ni" op (which would be
> and-immediate) which is used for the constant clear_bit
> implementation. Therefore s390 needs full barriers for the
> {before,after} atomic ops.
Good catch, if ni/oi are used this is required. What we want to
add is an #ifdef CONFIG_HAVE_MARCH_Z196_FEATURES. With smp_mb__*
defined as smp_mb() we get additional barriers for older machines
while the atomic ops are defined with compare-and-swap which
already does the barrier before and after the operation.
We can do that with a patch on top of this one, so no hurry.
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
prev parent reply other threads:[~2014-04-23 7:38 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-18 13:11 [tip:locking/core] arch,s390: Convert smp_mb__*() tip-bot for Peter Zijlstra
2014-04-23 7:37 ` Martin Schwidefsky [this message]
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