linux-kernel - Re: [PATCH v5 2/4] arch: Add lightweight memory barriers dma_rmb() and dma

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Message-ID: <1416957328.5089.17.camel@kernel.crashing.org>
Date:	Wed, 26 Nov 2014 10:15:28 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alexander Duyck <alexander.h.duyck@...hat.com>
Cc:	linux-arch@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, mathieu.desnoyers@...ymtl.ca,
	peterz@...radead.org, heiko.carstens@...ibm.com, mingo@...nel.org,
	mikey@...ling.org, linux@....linux.org.uk,
	donald.c.skidmore@...el.com, matthew.vick@...el.com,
	geert@...ux-m68k.org, jeffrey.t.kirsher@...el.com,
	romieu@...zoreil.com, paulmck@...ux.vnet.ibm.com,
	nic_swsd@...ltek.com, will.deacon@....com, michael@...erman.id.au,
	tony.luck@...el.com, torvalds@...ux-foundation.org,
	oleg@...hat.com, schwidefsky@...ibm.com, fweisbec@...il.com,
	davem@...emloft.net
Subject: Re: [PATCH v5 2/4] arch: Add lightweight memory barriers dma_rmb()
 and dma_wmb()

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@...nel.crashing.org>



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