[PATCH 3/4] mac80211: fix low throughput in push pull mode

[Yibo Zhao <yiboz@xxxxxxxxxxxxxx>]

If station is ineligible for transmission in ieee80211_txq_may_transmit(),
no packet will be delivered to FW. During the tests in push-pull mode with
many clients, after several seconds, not a single station is an eligible
candidate for transmission since global time is smaller than all the
station's virtual airtime. As a consequence, the Tx has been blocked and
throughput is quite low.

To avoid this situation to occur in push-pull mode, the new proposal is:

- Increase the airtime grace period a little more to reduce the
  unexpected sync

- If global virtual time is less than the virtual airtime of any station,
  sync it to the airtime of first station in the red-black tree

- Round the division result since the process of global virtual time
  involves the division calculation

Co-developed-by: Yibo Zhao <yiboz@xxxxxxxxxxxxxx>
Signed-off-by: Yibo Zhao <yiboz@xxxxxxxxxxxxxx>
Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxx>
---
 net/mac80211/sta_info.c |  3 ++-
 net/mac80211/sta_info.h |  2 +-
 net/mac80211/tx.c       | 16 +++++++++++++++-
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index 9d01fdd..feac975 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -1852,7 +1852,8 @@ void ieee80211_sta_register_airtime(struct ieee80211_sta *pubsta, u8 tid,
 
 	weight_sum = local->airtime_weight_sum[ac] ?: sta->airtime_weight;
 
-	local->airtime_v_t[ac] += airtime / weight_sum;
+	/* Round the calculation of global vt */
+	local->airtime_v_t[ac] += (airtime + (weight_sum >> 1)) / weight_sum;
 	sta->airtime[ac].v_t += airtime / sta->airtime_weight;
 	ieee80211_resort_txq(&local->hw, txq);
 
diff --git a/net/mac80211/sta_info.h b/net/mac80211/sta_info.h
index 5c1cac9..5055f94 100644
--- a/net/mac80211/sta_info.h
+++ b/net/mac80211/sta_info.h
@@ -130,7 +130,7 @@ enum ieee80211_agg_stop_reason {
 /* Debugfs flags to enable/disable use of RX/TX airtime in scheduler */
 #define AIRTIME_USE_TX		BIT(0)
 #define AIRTIME_USE_RX		BIT(1)
-#define AIRTIME_GRACE 500 /* usec of grace period before reset */
+#define AIRTIME_GRACE 2000 /* usec of grace period before reset */
 
 struct airtime_info {
 	u64 rx_airtime;
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 42ca010..60cf569 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -3867,15 +3867,29 @@ bool ieee80211_txq_may_transmit(struct ieee80211_hw *hw,
 				struct ieee80211_txq *txq)
 {
 	struct ieee80211_local *local = hw_to_local(hw);
-	struct txq_info *txqi = to_txq_info(txq);
+	struct txq_info *first_txqi, *txqi = to_txq_info(txq);
+	struct rb_node *node = NULL;
 	struct sta_info *sta;
 	u8 ac = txq->ac;
+	first_txqi = NULL;
 
 	lockdep_assert_held(&local->active_txq_lock[ac]);
 
 	if (!txqi->txq.sta)
 		return true;
 
+	node = rb_first_cached(&local->active_txqs[ac]);
+	if (node) {
+		first_txqi = container_of(node, struct txq_info,
+					  schedule_order);
+		if (first_txqi->txq.sta) {
+			sta = container_of(first_txqi->txq.sta,
+					   struct sta_info, sta);
+			if (local->airtime_v_t[ac] < sta->airtime[ac].v_t)
+				local->airtime_v_t[ac] = sta->airtime[ac].v_t;
+		}
+	}
+
 	sta = container_of(txqi->txq.sta, struct sta_info, sta);
 	return (sta->airtime[ac].v_t <= local->airtime_v_t[ac]);
 }
-- 
1.9.1