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SubjectRe: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines
On Tue, May 11, 2010 at 09:42:03AM +0300, Pekka Enberg wrote:
> Hi Dmitry,
>
> On Tue, May 11, 2010 at 9:33 AM, Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
> >> what guarantee exactly do you have for that statement ?
> >
> > The data is kmalloced, kmalloc aligns on cacheline boundary AFAIK which
> > means that next kmalloc data chunk will not share "our" cacheline.
>
> No, there are no such guarantees. kmalloc() aligns on
> ARCH_KMALLOC_MINALIGN or ARCH_SLAB_MINALIGN depending on which is
> bigger but beyond that, there are no guarantees. You can, of course,
> use kmem_cache_create() with SLAB_HWCACHE_ALIGN to align on cacheline
> boundary.
>

The architectures that we are trying to deal with here should be forcing
kmalloc to the cache boundary already though - otherwise they would not
be able to used kmalloced memory for DMA buffers at all. Or am I utterly
lost here?

--
Dmitry


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