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96012227e5
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>
133 lines
5.0 KiB
Diff
133 lines
5.0 KiB
Diff
From: Felix Fietkau <nbd@nbd.name>
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Date: Sat, 28 May 2022 16:44:53 +0200
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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
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whenever more than 8ms worth of airtime is reported.
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Bigger weight values impose even smaller limits on maximum airtime values.
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This can mess up airtime based calculations for drivers that don't report
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per-PPDU airtime values, but batch up values instead.
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Fix this by reordering multiplications/shifts and by reducing unnecessary
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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
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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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---
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--- a/net/mac80211/ieee80211_i.h
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+++ b/net/mac80211/ieee80211_i.h
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@@ -1666,50 +1666,34 @@ static inline struct airtime_info *to_ai
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/* To avoid divisions in the fast path, we keep pre-computed reciprocals for
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* airtime weight calculations. There are two different weights to keep track
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* of: The per-station weight and the sum of weights per phy.
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- *
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- * For the per-station weights (kept in airtime_info below), we use 32-bit
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- * reciprocals with a devisor of 2^19. This lets us keep the multiplications and
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- * divisions for the station weights as 32-bit operations at the cost of a bit
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- * of rounding error for high weights; but the choice of divisor keeps rounding
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- * errors <10% for weights <2^15, assuming no more than 8ms of airtime is
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- * reported at a time.
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- *
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- * For the per-phy sum of weights the values can get higher, so we use 64-bit
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- * operations for those with a 32-bit divisor, which should avoid any
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- * significant rounding errors.
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+ * The per-sta shift value supports weight values of 1-4096
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*/
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-#define IEEE80211_RECIPROCAL_DIVISOR_64 0x100000000ULL
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-#define IEEE80211_RECIPROCAL_SHIFT_64 32
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-#define IEEE80211_RECIPROCAL_DIVISOR_32 0x80000U
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-#define IEEE80211_RECIPROCAL_SHIFT_32 19
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+#define IEEE80211_RECIPROCAL_SHIFT_SUM 24
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+#define IEEE80211_RECIPROCAL_SHIFT_STA 12
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+#define IEEE80211_WEIGHT_SHIFT 8
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-static inline void airtime_weight_set(struct airtime_info *air_info, u16 weight)
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+static inline void airtime_weight_set(struct airtime_info *air_info, u32 weight)
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{
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+ weight = min_t(u32, weight, BIT(IEEE80211_RECIPROCAL_SHIFT_STA));
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if (air_info->weight == weight)
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return;
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air_info->weight = weight;
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- if (weight) {
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- air_info->weight_reciprocal =
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- IEEE80211_RECIPROCAL_DIVISOR_32 / weight;
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- } else {
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- air_info->weight_reciprocal = 0;
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- }
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+ if (weight)
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+ weight = BIT(IEEE80211_RECIPROCAL_SHIFT_STA) / weight;
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+ air_info->weight_reciprocal = weight;
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}
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static inline void airtime_weight_sum_set(struct airtime_sched_info *air_sched,
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- int weight_sum)
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+ u32 weight_sum)
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{
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if (air_sched->weight_sum == weight_sum)
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return;
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air_sched->weight_sum = weight_sum;
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- if (air_sched->weight_sum) {
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- air_sched->weight_sum_reciprocal = IEEE80211_RECIPROCAL_DIVISOR_64;
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- do_div(air_sched->weight_sum_reciprocal, air_sched->weight_sum);
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- } else {
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- air_sched->weight_sum_reciprocal = 0;
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- }
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+ if (weight_sum)
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+ weight_sum = BIT(IEEE80211_RECIPROCAL_SHIFT_SUM) / weight_sum;
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+ air_sched->weight_sum_reciprocal = weight_sum;
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}
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/* A problem when trying to enforce airtime fairness is that we want to divide
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--- a/net/mac80211/sta_info.c
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+++ b/net/mac80211/sta_info.c
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@@ -1894,9 +1894,9 @@ void ieee80211_register_airtime(struct i
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{
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struct ieee80211_sub_if_data *sdata = vif_to_sdata(txq->vif);
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struct ieee80211_local *local = sdata->local;
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- u64 weight_sum, weight_sum_reciprocal;
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struct airtime_sched_info *air_sched;
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struct airtime_info *air_info;
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+ u64 weight_sum_reciprocal;
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u32 airtime = 0;
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air_sched = &local->airtime[txq->ac];
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@@ -1907,27 +1907,21 @@ void ieee80211_register_airtime(struct i
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if (local->airtime_flags & AIRTIME_USE_RX)
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airtime += rx_airtime;
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- /* Weights scale so the unit weight is 256 */
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- airtime <<= 8;
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-
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spin_lock_bh(&air_sched->lock);
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air_info->tx_airtime += tx_airtime;
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air_info->rx_airtime += rx_airtime;
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- if (air_sched->weight_sum) {
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- weight_sum = air_sched->weight_sum;
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+ if (air_sched->weight_sum)
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weight_sum_reciprocal = air_sched->weight_sum_reciprocal;
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- } else {
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- weight_sum = air_info->weight;
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+ else
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weight_sum_reciprocal = air_info->weight_reciprocal;
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- }
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/* Round the calculation of global vt */
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- air_sched->v_t += (u64)((airtime + (weight_sum >> 1)) *
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- weight_sum_reciprocal) >> IEEE80211_RECIPROCAL_SHIFT_64;
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- air_info->v_t += (u32)((airtime + (air_info->weight >> 1)) *
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- air_info->weight_reciprocal) >> IEEE80211_RECIPROCAL_SHIFT_32;
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+ air_sched->v_t += ((u64)airtime * weight_sum_reciprocal) >>
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+ (IEEE80211_RECIPROCAL_SHIFT_SUM - IEEE80211_WEIGHT_SHIFT);
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+ air_info->v_t += (airtime * air_info->weight_reciprocal) >>
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+ (IEEE80211_RECIPROCAL_SHIFT_STA - IEEE80211_WEIGHT_SHIFT);
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ieee80211_resort_txq(&local->hw, txq);
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spin_unlock_bh(&air_sched->lock);
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