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 <[EMAIL PROTECTED]>
Signed-off-by: Shai Fultheim <[EMAIL PROTECTED]>
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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