[PATCH v2] wifi: mac80211: don't reset the TXQ scheduling round number

[Julius Bairaktaris <julius@bairaktaris.de>]

A round is ended when ieee80211_next_txq() meets a txq whose remembered
round number is the current one, meaning it has gone full circle.

When the AC exceeds the airtime limit, ieee80211_txq_schedule_start()
sets the round number to 0 to close the round. The next open round is
1. A txq from an earlier round 1 still remembers the "1", so the next
round stops on it and serves nothing.

Fix: use a separate open/closed flag and let the round number keep
counting.

Testing: ~4200 skipped selections per 20s without the fix and 20
skipped selections per 20s with the fix on ath11k (with my AQL series
applied) at BE 500/1000.

Fixes: 8e4bac067105 ("wifi: mac80211: add a per-PHY AQL limit to improve fairness")
Assisted-by: Claude:claude-opus-5
Signed-off-by: Julius Bairaktaris <julius@bairaktaris.de>
---
v2: rewrote the message
v1: https://lore.kernel.org/linux-wireless/20260908135224.754049-1-julius@bairaktaris.de/

 net/mac80211/ieee80211_i.h | 1 +
 net/mac80211/tx.c          | 8 ++++----
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 53b0b08d3459..65311340db40 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -1468,6 +1468,7 @@ struct ieee80211_local {
 	spinlock_t active_txq_lock[IEEE80211_NUM_ACS];
 	struct list_head active_txqs[IEEE80211_NUM_ACS];
 	u16 schedule_round[IEEE80211_NUM_ACS];
+	bool schedule_open[IEEE80211_NUM_ACS];
 
 	/* serializes ieee80211_handle_wake_tx_queue */
 	spinlock_t handle_wake_tx_queue_lock;
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index c33092960df2..c665ced9c05c 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -4122,7 +4122,7 @@ struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac)
 
 	spin_lock_bh(&local->active_txq_lock[ac]);
 
-	if (!local->schedule_round[ac])
+	if (!local->schedule_open[ac])
 		goto out;
 
  begin:
@@ -4347,12 +4347,12 @@ void ieee80211_txq_schedule_start(struct ieee80211_hw *hw, u8 ac)
 
 	spin_lock_bh(&local->active_txq_lock[ac]);
 
-	if (ieee80211_txq_schedule_airtime_check(local, ac)) {
+	local->schedule_open[ac] =
+		ieee80211_txq_schedule_airtime_check(local, ac);
+	if (local->schedule_open[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]);
-- 
2.53.0