linux-kernel - Re: [PATCH 1/3 v3] dma: document dma_{un}map_{single|sg}

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Date:	Wed, 5 Mar 2008 11:02:02 -0800
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	akepner@....com
Cc:	James Bottomley <James.Bottomley@...senpartnership.com>,
	Grant Grundler <grundler@...isc-linux.org>,
	Michael Ellerman <michael@...erman.id.au>,
	Tony Luck <tony.luck@...el.com>, Jes Sorensen <jes@....com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Roland Dreier <rdreier@...co.com>,
	David Miller <davem@...emloft.net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3 v3] dma: document dma_{un}map_{single|sg}_attrs() interface

On Wednesday, March 05, 2008 10:13 am akepner@....com wrote:
> On Fri, Feb 29, 2008 at 12:37:56PM -0600, James Bottomley wrote:
> > ....
> > To be honest, I still don't like the name.  SYNC_ON_WRITE is the SN2
> > implementation.  What it's actually doing is implementing strict
> > ordering semantics.  I think it should really be
> > DMA_ATTR_STRICT_ORDERING (with a corresponding
> > DMA_ATTR_RELAXED_ORDERING)....
>
> I've been thinking about a new name, but don't like
> DMA_ATTR_STRICT_ORDERING.
>
> What I'm trying to do is to establish order (across
> a NUMA fabric) of DMA to different memory regions, i.e.,
> DMA to memory region A forces all outstanding DMA (to
> memory regions B, C,....) to complete first.
>
> DMA_ATTR_STRICT_ORDERING sounds like a PCI thing to me,
> and this is a NUMA interconnect thing.

Well, we used to call it a DMA barrier back in the old days, so 
DMA_ATTR_BARRIER might work (or DMA_ATTR_INTERCONNECT_BARRIER if you want to 
be extra clear about what it's doing).

Jesse
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