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    SubjectRe: kmap_atomic_pfn for PCI BAR access?
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    On Thursday 26 June 2008 13:11, Jeremy Fitzhardinge wrote:
    > Dave Airlie wrote:

    > > doing tlb flush for iounmap is slow as all hell if you do it a lot,
    > > and we can't afford to mmap the whole aperture it can 1GB.
    >
    > Maybe Nick's vmap reimplementation would help here. It effectively
    > allows you to map stuff into the vmalloc space, and do lazy tlb flushes
    > to mitigate the cost of map/unmap. He posted the patches week or so ago.

    Yeah, it can _really_ help. I'd posted some performance numbers with
    the patch which might prompt you to take another look at ioremap.

    One thing I still haven't implemented in that patch are CPU-local
    mappings (which only require a local flush to flush)... I found that
    after the improvements I did implement, they didn't help much for
    my workloads, so I suspect you might find the same thing... But anyway
    if you really need the per-CPU mappings, it should be possible to
    implement rather generically in vmap layer.

    I would be very interested to know what sort of results you see with it
    (compared to kmap_atomic and compared to vanilla ioremap)

    Thanks,
    Nick


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