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mac80211: add airtime fairness rework/fixes
latency and short-term fairness is improved by fixing the tx queue sorting so that it considers the pending AQL budget Signed-off-by: Felix Fietkau <nbd@nbd.name>
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...el/mac80211/patches/subsys/330-mac80211-fix-overflow-issues-in-airtime-fairness-cod.patch
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| @@ -0,0 +1,132 @@ | ||
| From: Felix Fietkau <nbd@nbd.name> | ||
| Date: Sat, 28 May 2022 16:44:53 +0200 | ||
| Subject: [PATCH] mac80211: fix overflow issues in airtime fairness code | ||
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| The airtime weight calculation overflows with a default weight value of 256 | ||
| whenever more than 8ms worth of airtime is reported. | ||
| Bigger weight values impose even smaller limits on maximum airtime values. | ||
| This can mess up airtime based calculations for drivers that don't report | ||
| per-PPDU airtime values, but batch up values instead. | ||
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| Fix this by reordering multiplications/shifts and by reducing unnecessary | ||
| intermediate precision (which was lost in a later stage anyway). | ||
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| The new shift value limits the maximum weight to 4096, which should be more | ||
| than enough. Any values bigger than that will be clamped to the upper limit. | ||
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| Signed-off-by: Felix Fietkau <nbd@nbd.name> | ||
| --- | ||
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| --- a/net/mac80211/ieee80211_i.h | ||
| +++ b/net/mac80211/ieee80211_i.h | ||
| @@ -1666,50 +1666,34 @@ static inline struct airtime_info *to_ai | ||
| /* To avoid divisions in the fast path, we keep pre-computed reciprocals for | ||
| * airtime weight calculations. There are two different weights to keep track | ||
| * of: The per-station weight and the sum of weights per phy. | ||
| - * | ||
| - * For the per-station weights (kept in airtime_info below), we use 32-bit | ||
| - * reciprocals with a devisor of 2^19. This lets us keep the multiplications and | ||
| - * divisions for the station weights as 32-bit operations at the cost of a bit | ||
| - * of rounding error for high weights; but the choice of divisor keeps rounding | ||
| - * errors <10% for weights <2^15, assuming no more than 8ms of airtime is | ||
| - * reported at a time. | ||
| - * | ||
| - * For the per-phy sum of weights the values can get higher, so we use 64-bit | ||
| - * operations for those with a 32-bit divisor, which should avoid any | ||
| - * significant rounding errors. | ||
| + * The per-sta shift value supports weight values of 1-4096 | ||
| */ | ||
| -#define IEEE80211_RECIPROCAL_DIVISOR_64 0x100000000ULL | ||
| -#define IEEE80211_RECIPROCAL_SHIFT_64 32 | ||
| -#define IEEE80211_RECIPROCAL_DIVISOR_32 0x80000U | ||
| -#define IEEE80211_RECIPROCAL_SHIFT_32 19 | ||
| +#define IEEE80211_RECIPROCAL_SHIFT_SUM 24 | ||
| +#define IEEE80211_RECIPROCAL_SHIFT_STA 12 | ||
| +#define IEEE80211_WEIGHT_SHIFT 8 | ||
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| -static inline void airtime_weight_set(struct airtime_info *air_info, u16 weight) | ||
| +static inline void airtime_weight_set(struct airtime_info *air_info, u32 weight) | ||
| { | ||
| + weight = min_t(u32, weight, BIT(IEEE80211_RECIPROCAL_SHIFT_STA)); | ||
| if (air_info->weight == weight) | ||
| return; | ||
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| air_info->weight = weight; | ||
| - if (weight) { | ||
| - air_info->weight_reciprocal = | ||
| - IEEE80211_RECIPROCAL_DIVISOR_32 / weight; | ||
| - } else { | ||
| - air_info->weight_reciprocal = 0; | ||
| - } | ||
| + if (weight) | ||
| + weight = BIT(IEEE80211_RECIPROCAL_SHIFT_STA) / weight; | ||
| + air_info->weight_reciprocal = weight; | ||
| } | ||
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| static inline void airtime_weight_sum_set(struct airtime_sched_info *air_sched, | ||
| - int weight_sum) | ||
| + u32 weight_sum) | ||
| { | ||
| if (air_sched->weight_sum == weight_sum) | ||
| return; | ||
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| air_sched->weight_sum = weight_sum; | ||
| - if (air_sched->weight_sum) { | ||
| - air_sched->weight_sum_reciprocal = IEEE80211_RECIPROCAL_DIVISOR_64; | ||
| - do_div(air_sched->weight_sum_reciprocal, air_sched->weight_sum); | ||
| - } else { | ||
| - air_sched->weight_sum_reciprocal = 0; | ||
| - } | ||
| + if (weight_sum) | ||
| + weight_sum = BIT(IEEE80211_RECIPROCAL_SHIFT_SUM) / weight_sum; | ||
| + air_sched->weight_sum_reciprocal = weight_sum; | ||
| } | ||
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| /* A problem when trying to enforce airtime fairness is that we want to divide | ||
| --- a/net/mac80211/sta_info.c | ||
| +++ b/net/mac80211/sta_info.c | ||
| @@ -1894,9 +1894,9 @@ void ieee80211_register_airtime(struct i | ||
| { | ||
| struct ieee80211_sub_if_data *sdata = vif_to_sdata(txq->vif); | ||
| struct ieee80211_local *local = sdata->local; | ||
| - u64 weight_sum, weight_sum_reciprocal; | ||
| struct airtime_sched_info *air_sched; | ||
| struct airtime_info *air_info; | ||
| + u64 weight_sum_reciprocal; | ||
| u32 airtime = 0; | ||
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| air_sched = &local->airtime[txq->ac]; | ||
| @@ -1907,27 +1907,21 @@ void ieee80211_register_airtime(struct i | ||
| if (local->airtime_flags & AIRTIME_USE_RX) | ||
| airtime += rx_airtime; | ||
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| - /* Weights scale so the unit weight is 256 */ | ||
| - airtime <<= 8; | ||
| - | ||
| spin_lock_bh(&air_sched->lock); | ||
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| air_info->tx_airtime += tx_airtime; | ||
| air_info->rx_airtime += rx_airtime; | ||
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| - if (air_sched->weight_sum) { | ||
| - weight_sum = air_sched->weight_sum; | ||
| + if (air_sched->weight_sum) | ||
| weight_sum_reciprocal = air_sched->weight_sum_reciprocal; | ||
| - } else { | ||
| - weight_sum = air_info->weight; | ||
| + else | ||
| weight_sum_reciprocal = air_info->weight_reciprocal; | ||
| - } | ||
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| /* Round the calculation of global vt */ | ||
| - air_sched->v_t += (u64)((airtime + (weight_sum >> 1)) * | ||
| - weight_sum_reciprocal) >> IEEE80211_RECIPROCAL_SHIFT_64; | ||
| - air_info->v_t += (u32)((airtime + (air_info->weight >> 1)) * | ||
| - air_info->weight_reciprocal) >> IEEE80211_RECIPROCAL_SHIFT_32; | ||
| + air_sched->v_t += ((u64)airtime * weight_sum_reciprocal) >> | ||
| + (IEEE80211_RECIPROCAL_SHIFT_SUM - IEEE80211_WEIGHT_SHIFT); | ||
| + air_info->v_t += (airtime * air_info->weight_reciprocal) >> | ||
| + (IEEE80211_RECIPROCAL_SHIFT_STA - IEEE80211_WEIGHT_SHIFT); | ||
| ieee80211_resort_txq(&local->hw, txq); | ||
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| spin_unlock_bh(&air_sched->lock); |
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