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    SubjectRe: kmap_atomic_pfn for PCI BAR access?
    On Mon, 7 Jul 2008 16:53:54 +1000
    Nick Piggin <nickpiggin@yahoo.com.au> wrote:

    > 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...

    just to complicate things with ioremap() you have to deal with the
    various caching-coherency requirements.. making things lazy and per CPU
    complicates that a ton (and I suspect won't actually make things
    cheaper)

    --
    If you want to reach me at my work email, use arjan@linux.intel.com
    For development, discussion and tips for power savings,
    visit http://www.lesswatts.org


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