RE: [LKML] Re: [PATCH v3] ad7877: keep dma rx buffers in seperatecache lines

[Marc Gauthier]

Mike Frysinger wrote:
> 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
>
> assuming alpha and s390 handle cache coherency in hardware, it looks
> to me like the proposed assumption (kmalloc returns cachealigned
> pointers when cache management is in software) does not hold true.
>
> so should these other arches also be setting ARCH_KMALLOC_MINALIGN to
> L1_CACHE_BYTES ?

IMHO, yes.  It just makes sense to avoid false-sharing issues, not to
allocate unrelated blocks in the same cache line.

Also as it turns out (hope he doesn't me telling), Christian Zankel
recently found a bug that was fixed exactly that way, by setting
ARCH_KMALLOC_MINALIGN to L1_CACHE_BYTES for the Xtensa architecture.
(Too recent to have percolated to mainline.)

A lot of the above might be cache line aligned (?).

-Marc
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