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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