netdev - Re: [PATCH 2/4] arch: Add lightweight memory barriers fast_rmb() and fast

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Message-ID: <1416271412.18381.20.camel@kernel.crashing.org>
Date:	Tue, 18 Nov 2014 11:43:32 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alexander Duyck <alexander.h.duyck@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Peter Zijlstra <peterz@...radead.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Michael Neuling <mikey@...ling.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	donald.c.skidmore@...el.com, matthew.vick@...el.com,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	Francois Romieu <romieu@...zoreil.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	nic_swsd@...ltek.com, Will Deacon <will.deacon@....com>,
	Michael Ellerman <michael@...erman.id.au>,
	Tony Luck <tony.luck@...el.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH 2/4] arch: Add lightweight memory barriers fast_rmb()
 and fast_wmb()

On Mon, 2014-11-17 at 13:54 -0800, Alexander Duyck wrote:

> What would you think of the name "coherent_*mb()"?  I would prefer to 
> avoid dma in the name since, at least in my mind, that implies MMIO.

I'm lazy, I like typing less, so I like dma_* but I don't object to
coherent_* if at least one more person thinks it makes the semantics
clearer :)

> It also ties in well with dma_alloc_coherent/dma_free_coherent which is 
> what would typically be used to allocate the memory we would be using 
> the barrier to protect anyway.

Agreed.

> > And yes, in the same spirit, it would probably be good to try to
> > eventually get rid of the plain "*mb()" functions, and perhaps call
> > them "mmio_*mb()" to clarify that they are about ordering memory wrt
> > mmio.
> >
> > Hmm?
> >
> >                          Linus
> 
> I will work on pulling all of the coherent barrier cases out of using 
> the plain "*mb()" calls first.  We need to sort that out before we could 
> look at renaming the plain barrier functions.

Makes sense.

Cheers,
Ben.

> - Alex
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