Message-ID: <1416957328.5089.17.camel@kernel.crashing.org>
Subject: Re: [PATCH v5 2/4] arch: Add lightweight memory barriers dma_rmb()
 and dma_wmb()
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Alexander Duyck <alexander.h.duyck@redhat.com>
Cc: linux-arch@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, mathieu.desnoyers@polymtl.ca,
        peterz@infradead.org, heiko.carstens@de.ibm.com, mingo@kernel.org,
        mikey@neuling.org, linux@arm.linux.org.uk, donald.c.skidmore@intel.com,
        matthew.vick@intel.com, geert@linux-m68k.org,
        jeffrey.t.kirsher@intel.com, romieu@fr.zoreil.com,
        paulmck@linux.vnet.ibm.com, nic_swsd@realtek.com, will.deacon@arm.com,
        michael@ellerman.id.au, tony.luck@intel.com,
        torvalds@linux-foundation.org, oleg@redhat.com, schwidefsky@de.ibm.com,
        fweisbec@gmail.com, davem@davemloft.net
Date: Wed, 26 Nov 2014 10:15:28 +1100
In-Reply-To: <20141119012400.9563.21117.stgit@ahduyck-server>
References: <20141119012205.9563.95544.stgit@ahduyck-server>
	 <20141119012400.9563.21117.stgit@ahduyck-server>
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Sender: linux-kernel-owner@vger.kernel.org

On Tue, 2014-11-18 at 17:24 -0800, Alexander Duyck wrote:
> There are a number of situations where the mandatory barriers rmb() and
> wmb() are used to order memory/memory operations in the device drivers
> and those barriers are much heavier than they actually need to be.  For
> example in the case of PowerPC wmb() calls the heavy-weight sync
> instruction when for coherent memory operations all that is really needed
> is an lsync or eieio instruction.
>  .../...

For powerpc:

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>


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