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

[Peter Zijlstra]

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@xxxxxxxxx>
---
 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)
 {

-- 

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