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Commit eb1e011a authored by Johannes Berg's avatar Johannes Berg
Browse files

average: change to declare precision, not factor 



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: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarJohannes Berg <johannes.berg@intel.com>
parent 48cac18e

drivers/net/virtio_net.c

+1 −1
Original line number Diff line number Diff line
@@ -51,7 +51,7 @@ module_param(gso, bool, 0444); 
 * at once, the weight is chosen so that the EWMA will be insensitive to short-

 * term, transient changes in packet size.

 */

DECLARE_EWMA(pkt_len, 1, 64)

DECLARE_EWMA(pkt_len, 0, 64)



/* With mergeable buffers we align buffer address and use the low bits to

 * encode its true size. Buffer size is up to 1 page so we need to align to

drivers/net/wireless/ath/ath5k/ath5k.h

+1 −1
Original line number Diff line number Diff line
@@ -1252,7 +1252,7 @@ struct ath5k_statistics { 
#define ATH5K_TXQ_LEN_MAX	(ATH_TXBUF / 4)		/* bufs per queue */

#define ATH5K_TXQ_LEN_LOW	(ATH5K_TXQ_LEN_MAX / 2)	/* low mark */



DECLARE_EWMA(beacon_rssi, 1024, 8)

DECLARE_EWMA(beacon_rssi, 10, 8)



/* Driver state associated with an instance of a device */

struct ath5k_hw {

drivers/net/wireless/ralink/rt2x00/rt2x00.h

+1 −1
Original line number Diff line number Diff line
@@ -257,7 +257,7 @@ struct link_qual { 
	int tx_failed;

};



DECLARE_EWMA(rssi, 1024, 8)

DECLARE_EWMA(rssi, 10, 8)



/*

 * Antenna settings about the currently active link.

include/linux/average.h

+41 −20
Original line number Diff line number Diff line 
#ifndef _LINUX_AVERAGE_H

#define _LINUX_AVERAGE_H



/* 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 /* _LINUX_AVERAGE_H */

net/batman-adv/types.h

+1 −1
Original line number Diff line number Diff line
@@ -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