Re: [PATCH] [ppc64] watch IOMMU virtual merging

[Andi Kleen]

On Tue, Aug 03, 2004 at 07:45:51AM +1000, Benjamin Herrenschmidt wrote:

[adding linux-scsi with full quote]
> 
> Actually, we could tune the ratio between large allocs and small allocs,
> the real problem is the failure case. We can't really afford to break
> down a physical segment at the iommu level because that would increase
> the size of the SG list which can't be dealt at the upper level (we don't
> know how much space has been allocated and the HW may have limitations on
> the number of entries).
> 
> What we really need is a way for drivers to return the BIO upstream and
> ask for a split in case of iommu allocation error, but I've been told that
> would be horribly complex...

Not very, according to James B. It just needs driver changes.
I would like to have it too. 

-Andi
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