ath9k: Introduce airtime fairness scheduling between stations

This reworks the ath9k driver to schedule transmissions to connected
stations in a way that enforces airtime fairness between them. It
accomplishes this by measuring the time spent transmitting to or
receiving from a station at TX and RX completion, and accounting this to
a per-station, per-QoS level airtime deficit. Then, an FQ-CoDel based
deficit scheduler is employed at packet dequeue time, to control which
station gets the next transmission opportunity.

Airtime fairness can significantly improve the efficiency of the network
when station rates vary. The following throughput values are from a
simple three-station test scenario, where two stations operate at the
highest HT20 rate, and one station at the lowest, and the scheduler is
employed at the access point:

                  Before   /   After
Fast station 1:    19.17   /   25.09 Mbps
Fast station 2:    19.83   /   25.21 Mbps
Slow station:       2.58   /    1.77 Mbps
Total:             41.58   /   52.07 Mbps

The benefit of airtime fairness goes up the more stations are present.
In a 30-station test with one station artificially limited to 1 Mbps,
we have seen aggregate throughput go from 2.14 to 17.76 Mbps.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

1 files changed, 65 insertions, 0 deletions

diff --git a/drivers/net/wireless/ath/ath9k/recv.c b/drivers/net/wireless/ath/ath9k/recv.c
index fb4ba27d92b7..d79837fe333f 100644
--- a/drivers/net/wireless/ath/ath9k/recv.c
+++ b/drivers/net/wireless/ath/ath9k/recv.c
@@ -1002,6 +1002,70 @@ static void ath9k_apply_ampdu_details(struct ath_softc *sc,
 	}
 }
 
+static void ath_rx_count_airtime(struct ath_softc *sc,
+				 struct ath_rx_status *rs,
+				 struct sk_buff *skb)
+{
+	struct ath_node *an;
+	struct ath_acq *acq;
+	struct ath_vif *avp;
+	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
+	struct ath_hw *ah = sc->sc_ah;
+	struct ath_common *common = ath9k_hw_common(ah);
+	struct ieee80211_sta *sta;
+	struct ieee80211_rx_status *rxs;
+	const struct ieee80211_rate *rate;
+	bool is_sgi, is_40, is_sp;
+	int phy;
+	u16 len = rs->rs_datalen;
+	u32 airtime = 0;
+	u8 tidno, acno;
+
+	if (!ieee80211_is_data(hdr->frame_control))
+		return;
+
+	rcu_read_lock();
+
+	sta = ieee80211_find_sta_by_ifaddr(sc->hw, hdr->addr2, NULL);
+	if (!sta)
+		goto exit;
+	an = (struct ath_node *) sta->drv_priv;
+	avp = (struct ath_vif *) an->vif->drv_priv;
+	tidno = skb->priority & IEEE80211_QOS_CTL_TID_MASK;
+	acno = TID_TO_WME_AC(tidno);
+	acq = &avp->chanctx->acq[acno];
+
+	rxs = IEEE80211_SKB_RXCB(skb);
+
+	is_sgi = !!(rxs->flag & RX_FLAG_SHORT_GI);
+	is_40 = !!(rxs->flag & RX_FLAG_40MHZ);
+	is_sp = !!(rxs->flag & RX_FLAG_SHORTPRE);
+
+	if (!!(rxs->flag & RX_FLAG_HT)) {
+		/* MCS rates */
+
+		airtime += ath_pkt_duration(sc, rxs->rate_idx, len,
+					is_40, is_sgi, is_sp);
+	} else {
+
+		phy = IS_CCK_RATE(rs->rs_rate) ? WLAN_RC_PHY_CCK : WLAN_RC_PHY_OFDM;
+		rate = &common->sbands[rxs->band].bitrates[rxs->rate_idx];
+		airtime += ath9k_hw_computetxtime(ah, phy, rate->bitrate * 100,
+						len, rxs->rate_idx, is_sp);
+	}
+
+ 	if (!!(sc->airtime_flags & AIRTIME_USE_RX)) {
+		spin_lock_bh(&acq->lock);
+		an->airtime_deficit[acno] -= airtime;
+		if (an->airtime_deficit[acno] <= 0)
+			__ath_tx_queue_tid(sc, ATH_AN_2_TID(an, tidno));
+		spin_unlock_bh(&acq->lock);
+	}
+	ath_debug_airtime(sc, an, airtime, 0);
+exit:
+	rcu_read_unlock();
+}
+
 int ath_rx_tasklet(struct ath_softc *sc, int flush, bool hp)
 {
 	struct ath_rxbuf *bf;
@@ -1148,6 +1212,7 @@ int ath_rx_tasklet(struct ath_softc *sc, int flush, bool hp)
 		ath9k_antenna_check(sc, &rs);
 		ath9k_apply_ampdu_details(sc, &rs, rxs);
 		ath_debug_rate_stats(sc, &rs, skb);
+		ath_rx_count_airtime(sc, &rs, skb);
 
 		hdr = (struct ieee80211_hdr *)skb->data;
 		if (ieee80211_is_ack(hdr->frame_control))