The following commit has been merged in the master branch: commit a72fabed870be653703e3f48b327a28d3b64ad08 Author: Johannes Berg johannes.berg@intel.com Date: Wed Feb 15 09:49:26 2017 +0100

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.

Signed-off-by: Johannes Berg johannes.berg@intel.com Acked-by: David S. Miller davem@davemloft.net Signed-off-by: Johannes Berg johannes.berg@intel.com

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 05a83db..df5f494 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -49,7 +49,7 @@ 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 diff --git a/drivers/net/wireless/ath/ath5k/ath5k.h b/drivers/net/wireless/ath/ath5k/ath5k.h index 67fedb6..979800c 100644 --- a/drivers/net/wireless/ath/ath5k/ath5k.h +++ b/drivers/net/wireless/ath/ath5k/ath5k.h @@ -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 { diff --git a/drivers/net/wireless/ralink/rt2x00/rt2x00.h b/drivers/net/wireless/ralink/rt2x00/rt2x00.h index 26869b3..3407878 100644 --- a/drivers/net/wireless/ralink/rt2x00/rt2x00.h +++ b/drivers/net/wireless/ralink/rt2x00/rt2x00.h @@ -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. diff --git a/include/linux/average.h b/include/linux/average.h index d04aa58..7ddaf34 100644 --- a/include/linux/average.h +++ b/include/linux/average.h @@ -1,45 +1,66 @@ #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 */ diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h index 8f64a5c..66b25e4 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 diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h index 159a1a7..0e71843 100644 --- a/net/mac80211/ieee80211_i.h +++ b/net/mac80211/ieee80211_i.h @@ -428,7 +428,7 @@ struct ieee80211_sta_tx_tspec { bool downgraded; };

-DECLARE_EWMA(beacon_signal, 16, 4) +DECLARE_EWMA(beacon_signal, 4, 4)

struct ieee80211_if_managed { struct timer_list timer; diff --git a/net/mac80211/sta_info.h b/net/mac80211/sta_info.h index 71fa41a..90a2c4d 100644 --- a/net/mac80211/sta_info.h +++ b/net/mac80211/sta_info.h @@ -322,8 +322,8 @@ struct ieee80211_fast_rx { struct rcu_head rcu_head; };

-/* we use only values in the range 0-100, so pick a large factor */ -DECLARE_EWMA(mesh_fail_avg, 1048576, 8) +/* we use only values in the range 0-100, so pick a large precision */ +DECLARE_EWMA(mesh_fail_avg, 20, 8)

/** * struct mesh_sta - mesh STA information @@ -373,7 +373,7 @@ struct mesh_sta { struct ewma_mesh_fail_avg fail_avg; };

-DECLARE_EWMA(signal, 1024, 8) +DECLARE_EWMA(signal, 10, 8)

struct ieee80211_sta_rx_stats { unsigned long packets;