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    SubjectRe: [PATCH 21/21]: powerpc/cell spidernet DMA coalescing
    Date
    On Wednesday 11 October 2006 03:46, Geoff Levand wrote:
    > >
    > > The others look good, but this one complicates the code and doesn't have any benefit.  20
    > > for 21 isn't bad.
    >
    > Is the motivation for this change to improve performance by reducing the overhead
    > of the mapping calls?  If so, there may be some benefit for some systems.  Could
    > you please elaborate?
    >

    From what I understand, this patch drastically reduces the number of
    I/O PTEs that are needed in the iommu. With the current static IOMMU
    mapping, it should only make a difference during initialization, but
    any platform that uses a dynamic mapping of iommu entries will benefit
    a lot from it, because:

    - the card can do better prefetching of consecutive memory
    - there are more I/O ptes available for other drivers.

    Arnd <><
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