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    SubjectRe: PCI-DMA: Out of IOMMU space on x86-64 (Athlon64x2), with solution
    Andi Kleen wrote:
    > On Thursday 02 March 2006 13:16, Jeff Garzik wrote:
    >>>Yes I've been thinking about adding a new sleeping interface to the IOMMU
    >>>that would block for new space to handle this. If I did that - would
    >>>libata be able to use it?
    >>No :( We map inside a spin_lock_irqsave.
    > Would it be easily possible to change that or is it difficult?
    > Also with the blocking interface there might be possible deadlock issues
    > because it will be essentially similar to allocating memory during IO.
    > But I think it's probably safe.

    The SCSI layer submits stuff to libata inside spin_lock_irqsave(), and
    from there we DMA-map and send straight to hardware.

    So, changing the hot path to permit sleeping would be difficult and add
    needless complexity, IMO.

    I would rather pay the penalty of resubmitting if the
    map-inside-spinlock fails, than to slow down the hot path.


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