Re: [PATCH 2/3] dma: override "dma_flags_set_dmaflush" for sn-ia64

From: Jes Sorensen
Date: Wed Aug 22 2007 - 13:11:17 EST


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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