Re: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines

[Michal Simek]

Mike Frysinger wrote:
> On Tue, May 11, 2010 at 17:53, Dmitry Torokhov wrote:
> > On Tue, May 11, 2010 at 11:48:36PM +0200, Johannes Weiner wrote:
> > > On Tue, May 11, 2010 at 04:54:41PM -0400, Mike Frysinger wrote:
> > > > does the phrase "DMA safe buffer" imply cache alignment ?
> > > I guess that depends on the architectural requirements.  On x86,
> > > apparently, not so much.  On ARM, probably yes, as it's the
> > > requirement to properly maintain coherency.
> > It looks liek ARM (and a few others) do this:
> >
> > [dtor@hammer work]$ grep -r ARCH_KMALLOC_MINALIGN arch/
> > arch/sh/include/asm/page.h:#define ARCH_KMALLOC_MINALIGN        L1_CACHE_BYTES
> > arch/frv/include/asm/mem-layout.h:#define       ARCH_KMALLOC_MINALIGN           8
> > arch/powerpc/include/asm/page_32.h:#define ARCH_KMALLOC_MINALIGN        L1_CACHE_BYTES
> > arch/arm/include/asm/cache.h:#define ARCH_KMALLOC_MINALIGN      L1_CACHE_BYTES
> > arch/microblaze/include/asm/page.h:#define ARCH_KMALLOC_MINALIGN        L1_CACHE_BYTES
> > arch/mips/include/asm/mach-tx49xx/kmalloc.h: * All happy, no need to define ARCH_KMALLOC_MINALIGN
> > arch/mips/include/asm/mach-ip27/kmalloc.h: * All happy, no need to define ARCH_KMALLOC_MINALIGN
> > arch/mips/include/asm/mach-ip32/kmalloc.h:#define ARCH_KMALLOC_MINALIGN 32
> > arch/mips/include/asm/mach-ip32/kmalloc.h:#define ARCH_KMALLOC_MINALIGN 128
> > arch/mips/include/asm/mach-generic/kmalloc.h:#define ARCH_KMALLOC_MINALIGN      128
> > arch/avr32/include/asm/cache.h:#define ARCH_KMALLOC_MINALIGN    L1_CACHE_BYTES
>
> if ARCH_KMALLOC_MINALIGN is not defined, the current allocators default to:
>  slub - alignof(unsigned long long)
>  slab - alignof(unsigned long long)
>  slob - alignof(unsigned long)
> which for many arches can mean an alignment of merely 4 or 8
>
> lets look at the cacheline sizes for arches that dont set
> ARCH_KMALLOC_MINALIGN to L1_CACHE_BYTES:
>  - alplha - 32 or 64
>  - frv - 32 or 64
>  - blackfin - 32
>  - parisc - 32 or 64
>  - mn10300 - 16
>  - s390 - 256
>  - score - 16
>  - sparc - 32
>  - xtensa - 16 or 32

Just for completion.

microblaze - 16 or 32.

Michal

--
Michal Simek, Ing. (M.Eng)
PetaLogix - Linux Solutions for a Reconfigurable World
w: www.petalogix.com p: +61-7-30090663,+42-0-721842854 f: +61-7-30090663
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