Johannes Berg
2017-Feb-15 08:49 UTC
[PATCH] average: change to declare precision, not factor
From: Johannes Berg <johannes.berg at 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.
Signed-off-by: Johannes Berg <johannes.berg at intel.com>
---
Unless I hear any objections, I will take this through my tree.
---
drivers/net/virtio_net.c | 2 +-
drivers/net/wireless/ath/ath5k/ath5k.h | 2 +-
drivers/net/wireless/ralink/rt2x00/rt2x00.h | 2 +-
include/linux/average.h | 61 +++++++++++++++++++----------
net/batman-adv/types.h | 2 +-
net/mac80211/ieee80211_i.h | 2 +-
net/mac80211/sta_info.h | 6 +--
7 files changed, 49 insertions(+), 28 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 11e28530c83c..5e0cc9ec0f81 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 67fedb61fcc0..979800c6f57f 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 26869b3bef45..340787894c69 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 d04aa58280de..7ddaf340d2ac 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 8f64a5c01345..66b25e410a41 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 159a1a733725..0e718437d080 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 71fa41a1368a..90a2c4deb00c 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;
--
2.9.3
David Miller
2017-Feb-15 17:54 UTC
[PATCH] average: change to declare precision, not factor
From: Johannes Berg <johannes at sipsolutions.net> Date: Wed, 15 Feb 2017 09:49:26 +0100> From: Johannes Berg <johannes.berg at 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. > > Signed-off-by: Johannes Berg <johannes.berg at intel.com> > --- > Unless I hear any objections, I will take this through my tree.Acked-by: David S. Miller <davem at davemloft.net>
Apparently Analagous Threads
- [PATCH] average: change to declare precision, not factor
- [PATCH 5/8] linux: drop __bitwise__ everywhere
- [PATCH 1/4] virtio_net: use DECLARE_EWMA
- [PATCH 1/4] virtio_net: use DECLARE_EWMA
- [PATCH v2 1/2] compiler-gcc.h: add gnu_inline to all inline declarations