diff mbox

[maint,1/3] batman-adv: average: change to declare precision, not factor

Message ID 20170304153331.22420-1-sven@narfation.org
State Accepted, archived
Commit e094894311988bb4e5c24e2127eb9960a0133b89
Delegated to: Simon Wunderlich
Headers show

Commit Message

Sven Eckelmann March 4, 2017, 3:33 p.m. UTC
From: Johannes Berg <johannes.berg@intel.com>

Declaring the factor is counter-intuitive, and people are prone
to using small(-ish) values even when that makes no sense.

Change the DECLARE_EWMA() macro to take the fractional precision,
in bits, rather than a factor, and update all users.

While at it, add some more documentation.

Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
[sven@narfation.org: Added compatibility code]
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
 compat-include/linux/average.h | 67 +++++++++++++++++++++++++++---------------
 net/batman-adv/types.h         |  2 +-
 2 files changed, 45 insertions(+), 24 deletions(-)
diff mbox

Patch

diff --git a/compat-include/linux/average.h b/compat-include/linux/average.h
index ec022cb6..a1e3c254 100644
--- a/compat-include/linux/average.h
+++ b/compat-include/linux/average.h
@@ -26,49 +26,70 @@ 
 
 #include <linux/bug.h>
 
-#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 3, 0)
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 3, 0)
+#undef DECLARE_EWMA
+#endif /* < KERNEL_VERSION(4, 3, 0) */
 
-/* Exponentially weighted moving average (EWMA) */
+/*
+ * Exponentially weighted moving average (EWMA)
+ *
+ * This implements a fixed-precision EWMA algorithm, with both the
+ * precision and fall-off coefficient determined at compile-time
+ * and built into the generated helper funtions.
+ *
+ * The first argument to the macro is the name that will be used
+ * for the struct and helper functions.
+ *
+ * The second argument, the precision, expresses how many bits are
+ * used for the fractional part of the fixed-precision values.
+ *
+ * The third argument, the weight reciprocal, determines how the
+ * new values will be weighed vs. the old state, new values will
+ * get weight 1/weight_rcp and old values 1-1/weight_rcp. Note
+ * that this parameter must be a power of two for efficiency.
+ */
 
-#define DECLARE_EWMA(name, _factor, _weight)				\
+#define DECLARE_EWMA(name, _precision, _weight_rcp)			\
 	struct ewma_##name {						\
 		unsigned long internal;					\
 	};								\
 	static inline void ewma_##name##_init(struct ewma_##name *e)	\
 	{								\
-		BUILD_BUG_ON(!__builtin_constant_p(_factor));		\
-		BUILD_BUG_ON(!__builtin_constant_p(_weight));		\
-		BUILD_BUG_ON_NOT_POWER_OF_2(_factor);			\
-		BUILD_BUG_ON_NOT_POWER_OF_2(_weight);			\
+		BUILD_BUG_ON(!__builtin_constant_p(_precision));	\
+		BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp));	\
+		/*							\
+		 * Even if you want to feed it just 0/1 you should have	\
+		 * some bits for the non-fractional part...		\
+		 */							\
+		BUILD_BUG_ON((_precision) > 30);			\
+		BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp);		\
 		e->internal = 0;					\
 	}								\
 	static inline unsigned long					\
 	ewma_##name##_read(struct ewma_##name *e)			\
 	{								\
-		BUILD_BUG_ON(!__builtin_constant_p(_factor));		\
-		BUILD_BUG_ON(!__builtin_constant_p(_weight));		\
-		BUILD_BUG_ON_NOT_POWER_OF_2(_factor);			\
-		BUILD_BUG_ON_NOT_POWER_OF_2(_weight);			\
-		return e->internal >> ilog2(_factor);			\
+		BUILD_BUG_ON(!__builtin_constant_p(_precision));	\
+		BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp));	\
+		BUILD_BUG_ON((_precision) > 30);			\
+		BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp);		\
+		return e->internal >> (_precision);			\
 	}								\
 	static inline void ewma_##name##_add(struct ewma_##name *e,	\
 					     unsigned long val)		\
 	{								\
 		unsigned long internal = ACCESS_ONCE(e->internal);	\
-		unsigned long weight = ilog2(_weight);			\
-		unsigned long factor = ilog2(_factor);			\
+		unsigned long weight_rcp = ilog2(_weight_rcp);		\
+		unsigned long precision = _precision;			\
 									\
-		BUILD_BUG_ON(!__builtin_constant_p(_factor));		\
-		BUILD_BUG_ON(!__builtin_constant_p(_weight));		\
-		BUILD_BUG_ON_NOT_POWER_OF_2(_factor);			\
-		BUILD_BUG_ON_NOT_POWER_OF_2(_weight);			\
+		BUILD_BUG_ON(!__builtin_constant_p(_precision));	\
+		BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp));	\
+		BUILD_BUG_ON((_precision) > 30);			\
+		BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp);		\
 									\
 		ACCESS_ONCE(e->internal) = internal ?			\
-			(((internal << weight) - internal) +		\
-				(val << factor)) >> weight :		\
-			(val << factor);				\
+			(((internal << weight_rcp) - internal) +	\
+				(val << precision)) >> weight_rcp :	\
+			(val << precision);				\
 	}
 
-#endif /* < KERNEL_VERSION(4, 3, 0) */
-
 #endif /* _NET_BATMAN_ADV_COMPAT_LINUX_AVERAGE_H */
diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index 8f64a5c0..66b25e41 100644
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -402,7 +402,7 @@  struct batadv_gw_node {
 	struct rcu_head rcu;
 };
 
-DECLARE_EWMA(throughput, 1024, 8)
+DECLARE_EWMA(throughput, 10, 8)
 
 /**
  * struct batadv_hardif_neigh_node_bat_v - B.A.T.M.A.N. V private neighbor