diff options
Diffstat (limited to 'arch/tile/include/asm/cache.h')
| -rw-r--r-- | arch/tile/include/asm/cache.h | 25 |
1 files changed, 19 insertions, 6 deletions
diff --git a/arch/tile/include/asm/cache.h b/arch/tile/include/asm/cache.h index 392e5333dd8..6160761d5f6 100644 --- a/arch/tile/include/asm/cache.h +++ b/arch/tile/include/asm/cache.h @@ -27,11 +27,17 @@ #define L2_CACHE_ALIGN(x) (((x)+(L2_CACHE_BYTES-1)) & -L2_CACHE_BYTES) /* - * TILE-Gx is fully coherent so we don't need to define ARCH_DMA_MINALIGN. + * TILEPro I/O is not always coherent (networking typically uses coherent + * I/O, but PCI traffic does not) and setting ARCH_DMA_MINALIGN to the + * L2 cacheline size helps ensure that kernel heap allocations are aligned. + * TILE-Gx I/O is always coherent when used on hash-for-home pages. + * + * However, it's possible at runtime to request not to use hash-for-home + * for the kernel heap, in which case the kernel will use flush-and-inval + * to manage coherence. As a result, we use L2_CACHE_BYTES for the + * DMA minimum alignment to avoid false sharing in the kernel heap. */ -#ifndef __tilegx__ #define ARCH_DMA_MINALIGN L2_CACHE_BYTES -#endif /* use the cache line size for the L2, which is where it counts */ #define SMP_CACHE_BYTES_SHIFT L2_CACHE_SHIFT @@ -43,9 +49,16 @@ #define __read_mostly __attribute__((__section__(".data..read_mostly"))) /* - * Attribute for data that is kept read/write coherent until the end of - * initialization, then bumped to read/only incoherent for performance. + * Originally we used small TLB pages for kernel data and grouped some + * things together as "write once", enforcing the property at the end + * of initialization by making those pages read-only and non-coherent. + * This allowed better cache utilization since cache inclusion did not + * need to be maintained. However, to do this requires an extra TLB + * entry, which on balance is more of a performance hit than the + * non-coherence is a performance gain, so we now just make "read + * mostly" and "write once" be synonyms. We keep the attribute + * separate in case we change our minds at a future date. */ -#define __write_once __attribute__((__section__(".w1data"))) +#define __write_once __read_mostly #endif /* _ASM_TILE_CACHE_H */ |