linux-kernel - Re: [PATCH 2/3] dma: override "dma_flags_set

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Message-ID: <46CC6C4B.1030202@sgi.com>
Date:	Wed, 22 Aug 2007 19:03:07 +0200
From:	Jes Sorensen <jes@....com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>, akepner@....com,
	Randy Dunlap <randy.dunlap@...cle.com>,
	linux-kernel <linux-kernel@...r.kernel.org>, rdreier@...co.com,
	linux-ia64 <linux-ia64@...r.kernel.org>
Subject: Re: [PATCH 2/3] dma: override "dma_flags_set_dmaflush" for sn-ia64

James Bottomley wrote:
> I really don't think a work around for a PCI spec violation belongs in
> the generic DMA code, do you?  The correct fix for this should be to set
> the device hints to strict ordering, which presumably altix respects?
> In which case, it sounds like what needs exposing are access to the PCI
> device hints.  I believe both PCI-X and PCIe have these hints as
> optional specifiers in the bridges, so it should be in a current Rev of
> the PCI spec.  Or are you proposing adding an additional PCI API that
> allows transaction flushes to be inserted into the stream for devices
> and bridges that have already negotiated relaxed ordering? ... in which
> case we need to take this to the PCI list.

James,

I don't believe it respects those hints - I agree, it's a pita, but
thats the state of the situation. Even if it did, it would make
performance suck as Jesse also pointed out.

As I pointed out in my email to Willy is that the NUMA fabric is routed,
there's not one path through the system, which is what makes this
happen.

Jes
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