On Thu, May 19, 2011 at 7:36 PM, Benjamin Herrenschmidt
<b...@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.
-eric
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