mac80211: add airtime fairness improvements

This reverts the airtime scheduler back from the virtual-time based scheduler
to the deficit round robin scheduler implementation.
This reduces burstiness and improves fairness by improving interaction with AQL.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/kernel/mac80211/patches/subsys/331-mac80211-make-sta-airtime-deficit-field-s32-instead-.patch

@@ -0,0 +1,52 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Mon, 20 Jun 2022 14:53:04 +0200
+Subject: [PATCH] mac80211: make sta airtime deficit field s32 instead of
+ s64
+
+32 bit is more than enough range for the airtime deficit
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/mac80211/debugfs_sta.c
++++ b/net/mac80211/debugfs_sta.c
+@@ -202,7 +202,7 @@ static ssize_t sta_airtime_read(struct f
+ 	size_t bufsz = 400;
+ 	char *buf = kzalloc(bufsz, GFP_KERNEL), *p = buf;
+ 	u64 rx_airtime = 0, tx_airtime = 0;
+-	s64 deficit[IEEE80211_NUM_ACS];
++	s32 deficit[IEEE80211_NUM_ACS];
+ 	ssize_t rv;
+ 	int ac;
+
+@@ -219,7 +219,7 @@ static ssize_t sta_airtime_read(struct f
+
+ 	p += scnprintf(p, bufsz + buf - p,
+ 		"RX: %llu us\nTX: %llu us\nWeight: %u\n"
+-		"Deficit: VO: %lld us VI: %lld us BE: %lld us BK: %lld us\n",
++		"Deficit: VO: %d us VI: %d us BE: %d us BK: %d us\n",
+ 		rx_airtime, tx_airtime, sta->airtime_weight,
+ 		deficit[0], deficit[1], deficit[2], deficit[3]);
+
+--- a/net/mac80211/sta_info.h
++++ b/net/mac80211/sta_info.h
+@@ -138,7 +138,7 @@ enum ieee80211_agg_stop_reason {
+ struct airtime_info {
+ 	u64 rx_airtime;
+ 	u64 tx_airtime;
+-	s64 deficit;
++	s32 deficit;
+ 	atomic_t aql_tx_pending; /* Estimated airtime for frames pending */
+ 	u32 aql_limit_low;
+ 	u32 aql_limit_high;
+--- a/net/mac80211/tx.c
++++ b/net/mac80211/tx.c
+@@ -3847,7 +3847,7 @@ struct ieee80211_txq *ieee80211_next_txq
+ 		struct sta_info *sta = container_of(txqi->txq.sta,
+ 						    struct sta_info, sta);
+ 		bool aql_check = ieee80211_txq_airtime_check(hw, &txqi->txq);
+-		s64 deficit = sta->airtime[txqi->txq.ac].deficit;
++		s32 deficit = sta->airtime[txqi->txq.ac].deficit;
+
+ 		if (aql_check)
+ 			found_eligible_txq = true;

package/kernel/mac80211/patches/subsys/332-mac80211-consider-aql_tx_pending-when-checking-airti.patch

@@ -0,0 +1,48 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Mon, 20 Jun 2022 14:59:09 +0200
+Subject: [PATCH] mac80211: consider aql_tx_pending when checking airtime
+ deficit
+
+When queueing packets for a station, deficit only gets added once the packets
+have been transmitted, which could be much later. During that time, a lot of
+temporary unfairness could happen, which could lead to bursty behavior.
+Fix this by subtracting the aql_tx_pending when checking the deficit in tx
+scheduling.
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/mac80211/tx.c
++++ b/net/mac80211/tx.c
+@@ -3817,6 +3817,13 @@ out:
+ }
+ EXPORT_SYMBOL(ieee80211_tx_dequeue);
+
++static inline s32 ieee80211_sta_deficit(struct sta_info *sta, u8 ac)
++{
++	struct airtime_info *air_info = &sta->airtime[ac];
++
++	return air_info->deficit - atomic_read(&air_info->aql_tx_pending);
++}
++
+ struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac)
+ {
+ 	struct ieee80211_local *local = hw_to_local(hw);
+@@ -3847,7 +3854,7 @@ struct ieee80211_txq *ieee80211_next_txq
+ 		struct sta_info *sta = container_of(txqi->txq.sta,
+ 						    struct sta_info, sta);
+ 		bool aql_check = ieee80211_txq_airtime_check(hw, &txqi->txq);
+-		s32 deficit = sta->airtime[txqi->txq.ac].deficit;
++		s32 deficit = ieee80211_sta_deficit(sta, txqi->txq.ac);
+
+ 		if (aql_check)
+ 			found_eligible_txq = true;
+@@ -3972,7 +3979,7 @@ bool ieee80211_txq_may_transmit(struct i
+ 			continue;
+ 		}
+ 		sta = container_of(iter->txq.sta, struct sta_info, sta);
+-		if (sta->airtime[ac].deficit < 0)
++		if (ieee80211_sta_deficit(sta, ac) < 0)
+ 			sta->airtime[ac].deficit += sta->airtime_weight;
+ 		list_move_tail(&iter->schedule_order, &local->active_txqs[ac]);
+ 	}

package/kernel/mac80211/patches/subsys/333-mac80211-keep-recently-active-tx-queues-in-schedulin.patch

@@ -0,0 +1,118 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Mon, 20 Jun 2022 20:52:50 +0200
+Subject: [PATCH] mac80211: keep recently active tx queues in scheduling
+ list
+
+This allows proper deficit accounting to ensure that they don't carry their
+deficit until the next time they become active
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/mac80211/ieee80211_i.h
++++ b/net/mac80211/ieee80211_i.h
+@@ -83,6 +83,13 @@ extern const u8 ieee80211_ac_to_qos_mask
+
+ #define IEEE80211_MAX_NAN_INSTANCE_ID 255
+
++
++/*
++ * Keep a station's queues on the active list for deficit accounting purposes
++ * if it was active or queued during the last 100ms
++ */
++#define AIRTIME_ACTIVE_DURATION (HZ / 10)
++
+ struct ieee80211_bss {
+ 	u32 device_ts_beacon, device_ts_presp;
+
+--- a/net/mac80211/sta_info.h
++++ b/net/mac80211/sta_info.h
+@@ -138,6 +138,7 @@ enum ieee80211_agg_stop_reason {
+ struct airtime_info {
+ 	u64 rx_airtime;
+ 	u64 tx_airtime;
++	u32 last_active;
+ 	s32 deficit;
+ 	atomic_t aql_tx_pending; /* Estimated airtime for frames pending */
+ 	u32 aql_limit_low;
+--- a/net/mac80211/tx.c
++++ b/net/mac80211/tx.c
+@@ -3824,6 +3824,36 @@ static inline s32 ieee80211_sta_deficit(
+ 	return air_info->deficit - atomic_read(&air_info->aql_tx_pending);
+ }
+
++static void
++ieee80211_txq_set_active(struct txq_info *txqi)
++{
++	struct sta_info *sta;
++
++	if (!txqi->txq.sta)
++		return;
++
++	sta = container_of(txqi->txq.sta, struct sta_info, sta);
++	sta->airtime[txqi->txq.ac].last_active = (u32)jiffies;
++}
++
++static bool
++ieee80211_txq_keep_active(struct txq_info *txqi)
++{
++	struct sta_info *sta;
++	u32 diff;
++
++	if (!txqi->txq.sta)
++		return false;
++
++	sta = container_of(txqi->txq.sta, struct sta_info, sta);
++	if (ieee80211_sta_deficit(sta, txqi->txq.ac) >= 0)
++		return false;
++
++	diff = (u32)jiffies - sta->airtime[txqi->txq.ac].last_active;
++
++	return diff <= AIRTIME_ACTIVE_DURATION;
++}
++
+ struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac)
+ {
+ 	struct ieee80211_local *local = hw_to_local(hw);
+@@ -3870,7 +3900,6 @@ struct ieee80211_txq *ieee80211_next_txq
+ 		}
+ 	}
+
+-
+ 	if (txqi->schedule_round == local->schedule_round[ac])
+ 		goto out;
+
+@@ -3890,12 +3919,13 @@ void __ieee80211_schedule_txq(struct iee
+ {
+ 	struct ieee80211_local *local = hw_to_local(hw);
+ 	struct txq_info *txqi = to_txq_info(txq);
++	bool has_queue;
+
+ 	spin_lock_bh(&local->active_txq_lock[txq->ac]);
+
++	has_queue = force || txq_has_queue(txq);
+ 	if (list_empty(&txqi->schedule_order) &&
+-	    (force || !skb_queue_empty(&txqi->frags) ||
+-	     txqi->tin.backlog_packets)) {
++	    (has_queue || ieee80211_txq_keep_active(txqi))) {
+ 		/* If airtime accounting is active, always enqueue STAs at the
+ 		 * head of the list to ensure that they only get moved to the
+ 		 * back by the airtime DRR scheduler once they have a negative
+@@ -3903,7 +3933,7 @@ void __ieee80211_schedule_txq(struct iee
+ 		 * get immediately moved to the back of the list on the next
+ 		 * call to ieee80211_next_txq().
+ 		 */
+-		if (txqi->txq.sta && local->airtime_flags &&
++		if (txqi->txq.sta && local->airtime_flags && has_queue &&
+ 		    wiphy_ext_feature_isset(local->hw.wiphy,
+ 					    NL80211_EXT_FEATURE_AIRTIME_FAIRNESS))
+ 			list_add(&txqi->schedule_order,
+@@ -3911,6 +3941,8 @@ void __ieee80211_schedule_txq(struct iee
+ 		else
+ 			list_add_tail(&txqi->schedule_order,
+ 				      &local->active_txqs[txq->ac]);
++		if (has_queue)
++			ieee80211_txq_set_active(txqi);
+ 	}
+
+ 	spin_unlock_bh(&local->active_txq_lock[txq->ac]);

package/kernel/mac80211/patches/subsys/334-mac80211-add-a-per-PHY-AQL-limit-to-improve-fairness.patch

@@ -0,0 +1,131 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Mon, 20 Jun 2022 21:26:34 +0200
+Subject: [PATCH] mac80211: add a per-PHY AQL limit to improve fairness
+
+In order to maintain fairness, the amount of queueing needs to be limited
+beyond the simple per-station AQL budget, otherwise the driver can simply
+repeatedly do scheduling rounds until all queues that have not used their
+AQL budget become eligble.
+
+To be conservative, use the high AQL limit for the first txq and add half
+of the low AQL for each subsequent queue.
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/mac80211/ieee80211_i.h
++++ b/net/mac80211/ieee80211_i.h
+@@ -1211,6 +1211,7 @@ struct ieee80211_local {
+ 	u32 aql_txq_limit_high[IEEE80211_NUM_ACS];
+ 	u32 aql_threshold;
+ 	atomic_t aql_total_pending_airtime;
++	atomic_t aql_ac_pending_airtime[IEEE80211_NUM_ACS];
+
+ 	const struct ieee80211_ops *ops;
+
+--- a/net/mac80211/main.c
++++ b/net/mac80211/main.c
+@@ -712,6 +712,7 @@ struct ieee80211_hw *ieee80211_alloc_hw_
+ 		local->aql_txq_limit_low[i] = IEEE80211_DEFAULT_AQL_TXQ_LIMIT_L;
+ 		local->aql_txq_limit_high[i] =
+ 			IEEE80211_DEFAULT_AQL_TXQ_LIMIT_H;
++		atomic_set(&local->aql_ac_pending_airtime[i], 0);
+ 	}
+
+ 	local->airtime_flags = AIRTIME_USE_TX | AIRTIME_USE_RX;
+--- a/net/mac80211/sta_info.c
++++ b/net/mac80211/sta_info.c
+@@ -1929,6 +1929,7 @@ void ieee80211_sta_update_pending_airtim
+ 				   &sta->airtime[ac].aql_tx_pending);
+
+ 		atomic_add(tx_airtime, &local->aql_total_pending_airtime);
++		atomic_add(tx_airtime, &local->aql_ac_pending_airtime[ac]);
+ 		return;
+ 	}
+
+@@ -1940,14 +1941,17 @@ void ieee80211_sta_update_pending_airtim
+ 				       tx_pending, 0);
+ 	}
+
++	atomic_sub(tx_airtime, &local->aql_total_pending_airtime);
+ 	tx_pending = atomic_sub_return(tx_airtime,
+-				       &local->aql_total_pending_airtime);
++				       &local->aql_ac_pending_airtime[ac]);
+ 	if (WARN_ONCE(tx_pending < 0,
+ 		      "Device %s AC %d pending airtime underflow: %u, %u",
+ 		      wiphy_name(local->hw.wiphy), ac, tx_pending,
+-		      tx_airtime))
+-		atomic_cmpxchg(&local->aql_total_pending_airtime,
++		      tx_airtime)) {
++		atomic_cmpxchg(&local->aql_ac_pending_airtime[ac],
+ 			       tx_pending, 0);
++		atomic_sub(tx_pending, &local->aql_total_pending_airtime);
++	}
+ }
+
+ int sta_info_move_state(struct sta_info *sta,
+--- a/net/mac80211/tx.c
++++ b/net/mac80211/tx.c
+@@ -3863,6 +3863,9 @@ struct ieee80211_txq *ieee80211_next_txq
+
+ 	spin_lock_bh(&local->active_txq_lock[ac]);
+
++	if (!local->schedule_round[ac])
++		goto out;
++
+  begin:
+ 	txqi = list_first_entry_or_null(&local->active_txqs[ac],
+ 					struct txq_info,
+@@ -3984,6 +3987,25 @@ bool ieee80211_txq_airtime_check(struct
+ }
+ EXPORT_SYMBOL(ieee80211_txq_airtime_check);
+
++static bool
++ieee80211_txq_schedule_airtime_check(struct ieee80211_local *local, u8 ac)
++{
++	unsigned int num_txq = 0;
++	struct txq_info *txq;
++	u32 aql_limit;
++
++	if (!wiphy_ext_feature_isset(local->hw.wiphy, NL80211_EXT_FEATURE_AQL))
++		return true;
++
++	list_for_each_entry(txq, &local->active_txqs[ac], schedule_order)
++		num_txq++;
++
++	aql_limit = (num_txq - 1) * local->aql_txq_limit_low[ac] / 2 +
++		    local->aql_txq_limit_high[ac];
++
++	return atomic_read(&local->aql_ac_pending_airtime[ac]) < aql_limit;
++}
++
+ bool ieee80211_txq_may_transmit(struct ieee80211_hw *hw,
+ 				struct ieee80211_txq *txq)
+ {
+@@ -4000,6 +4022,9 @@ bool ieee80211_txq_may_transmit(struct i
+ 	if (list_empty(&txqi->schedule_order))
+ 		goto out;
+
++	if (!ieee80211_txq_schedule_airtime_check(local, ac))
++		goto out;
++
+ 	list_for_each_entry_safe(iter, tmp, &local->active_txqs[ac],
+ 				 schedule_order) {
+ 		if (iter == txqi)
+@@ -4039,7 +4064,15 @@ void ieee80211_txq_schedule_start(struct
+ 	struct ieee80211_local *local = hw_to_local(hw);
+
+ 	spin_lock_bh(&local->active_txq_lock[ac]);
+-	local->schedule_round[ac]++;
++
++	if (ieee80211_txq_schedule_airtime_check(local, ac)) {
++		local->schedule_round[ac]++;
++		if (!local->schedule_round[ac])
++			local->schedule_round[ac]++;
++	} else {
++		local->schedule_round[ac] = 0;
++	}
++
+ 	spin_unlock_bh(&local->active_txq_lock[ac]);
+ }
+ EXPORT_SYMBOL(ieee80211_txq_schedule_start);