Messages in this thread Patch in this message | | | Date | Tue, 15 Mar 2005 21:05:38 -0800 (PST) | From | Christoph Lameter <> | Subject | Re: [PATCH] Replace zone padding with a definition in cache.h |
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On Wed, 16 Mar 2005, Nick Piggin wrote:
> > > > +#ifndef ____cacheline_pad_in_smp > > +#if defined(CONFIG_SMP) > > +#define ____cacheline_pad_in_smp struct { char x; } ____cacheline_maxaligned_in_smp > ^^^^^^^ > > Doesn't this add a redundant cacheline if the padding is > previously perfect? Because of the extra byte you're adding? > > IIRC, the char x[0]; trick does the job correctly.
Good idea.
This patch removes the zone padding hack and establishes definitions in include/linux/cache.h to define the padding within struct zone.
Signed-off-by: Christoph Lameter <christoph@lameter.com> Signed-off-by: Shai Fultheim <Shai@Scalex86.org>
Index: linux-2.6.11/include/linux/cache.h =================================================================== --- linux-2.6.11.orig/include/linux/cache.h 2005-03-08 18:40:15.000000000 -0800 +++ linux-2.6.11/include/linux/cache.h 2005-03-14 10:33:45.247701040 -0800 @@ -48,4 +48,12 @@ #endif #endif
+#ifndef ____cacheline_pad_in_smp +#if defined(CONFIG_SMP) +#define ____cacheline_pad_in_smp struct { char x[0]; } ____cacheline_maxaligned_in_smp +#else +#define ____cacheline_pad_in_smp +#endif +#endif + #endif /* __LINUX_CACHE_H */ Index: linux-2.6.11/include/linux/mmzone.h =================================================================== --- linux-2.6.11.orig/include/linux/mmzone.h 2005-03-14 10:33:01.037422024 -0800 +++ linux-2.6.11/include/linux/mmzone.h 2005-03-14 10:33:45.248700888 -0800 @@ -28,21 +28,6 @@ struct free_area {
struct pglist_data;
-/* - * zone->lock and zone->lru_lock are two of the hottest locks in the kernel. - * So add a wild amount of padding here to ensure that they fall into separate - * cachelines. There are very few zone structures in the machine, so space - * consumption is not a concern here. - */ -#if defined(CONFIG_SMP) -struct zone_padding { - char x[0]; -} ____cacheline_maxaligned_in_smp; -#define ZONE_PADDING(name) struct zone_padding name; -#else -#define ZONE_PADDING(name) -#endif - struct per_cpu_pages { int count; /* number of pages in the list */ int low; /* low watermark, refill needed */ @@ -131,7 +116,14 @@ struct zone { struct free_area free_area[MAX_ORDER];
- ZONE_PADDING(_pad1_) + /* + * zone->lock and zone->lru_lock are two of the hottest locks in the kernel. + * So add a wild amount of padding here to ensure that they fall into separate + * cachelines. There are very few zone structures in the machine, so space + * consumption is not a concern here. + */ + + ____cacheline_pad_in_smp;
/* Fields commonly accessed by the page reclaim scanner */ spinlock_t lru_lock; @@ -164,7 +156,7 @@ struct zone { int prev_priority;
- ZONE_PADDING(_pad2_) + ____cacheline_pad_in_smp; /* Rarely used or read-mostly fields */
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