Subject: [PATCH] mac80211: keep recently active tx queues in scheduling list
From: Felix Fietkau <[email-masked]>
Date: Mon, 20 Jun 2022 20:52:50 +0200

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 <[email-masked]>
---

--- 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
@@ -3826,6 +3826,36 @@ 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);
@@ -3872,7 +3902,6 @@ struct ieee80211_txq *ieee80211_next_txq
 		}
 	}
 
-
 	if (txqi->schedule_round == local->schedule_round[ac])
 		goto out;
 
@@ -3892,12 +3921,13 @@ 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
@@ -3905,7 +3935,7 @@ 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,
@@ -3913,6 +3943,8 @@ 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]);