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    SubjectRe: [PATCH 5/7] [RFC] force 32-byte aligned kmallocs
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    On Thu, 2011-05-19 at 19:47 -0500, Eric Van Hensbergen wrote:
    > On Thu, May 19, 2011 at 7:36 PM, Benjamin Herrenschmidt
    > <benh@kernel.crashing.org> wrote:
    > > On Wed, 2011-05-18 at 16:24 -0500, Eric Van Hensbergen wrote:
    > >>
    > >> -#ifdef CONFIG_NOT_COHERENT_CACHE
    > >> +#if defined(CONFIG_NOT_COHERENT_CACHE) || defined(CONFIG_BGP)
    > >> #define ARCH_DMA_MINALIGN L1_CACHE_BYTES
    > >> #endif
    > >
    > > Is DMA cache coherent on BG/P ? That's odd for a 4xx base :-)
    > >
    >
    > My understanding of things (which could be totally wrong) is that the
    > DMA we care about on BG/P (namely the Torus and Collective networks)
    > is coherent at the L2. Of course the change in question is talking
    > about L1_CACHE_BYTES, so my reading of this is that its a sleazy way
    > of getting aligned mallocs that make interactions with the tightly
    > coupled networks easier/more-efficient. I'm open to alternative
    > suggestions.

    But if it's not coherent with L1, then you sould have
    CONFIG_NOT_COHERENT_CACHE set and not need that patch... or am I missing
    something ?

    One thing we should do some day as well is make that whole non-coherent
    be runtime selected, on the list of things to fix 440+47x in the same
    kernel. Pfiew....

    Cheers,
    Ben.



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