[PATCH 03/12] lib: dampen the percpu_counter FBC_BATCH

Peter Zijlstra
2007-04-17T07:10:49Z

[-- Attachment #1: percpu_counter_batch.patch --]
[-- Type: text/plain, Size: 1174 bytes --]

With the current logic the percpu_counter's accuracy delta is quadric
wrt the number of cpus in the system, reduce this to O(n ln n).

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
include/linux/percpu_counter.h | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

Index: linux-2.6-mm/include/linux/percpu_counter.h
===================================================================
--- linux-2.6-mm.orig/include/linux/percpu_counter.h
+++ linux-2.6-mm/include/linux/percpu_counter.h
@@ -11,6 +11,7 @@
#include <linux/threads.h>
#include <linux/percpu.h>
#include <linux/types.h>
+#include <linux/log2.h>

#ifdef CONFIG_SMP

@@ -20,11 +21,7 @@ struct percpu_counter {
s32 *counters;
};

-#if NR_CPUS >= 16
-#define FBC_BATCH (NR_CPUS*2)
-#else
-#define FBC_BATCH (NR_CPUS*4)
-#endif
+#define FBC_BATCH (8*ilog2(NR_CPUS))

static inline void percpu_counter_init(struct percpu_counter *fbc, s64 amount)
{