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, 54 insertions, 0 deletions

diff --git a/drivers/net/wireless/ath/ath9k/debug_sta.c b/drivers/net/wireless/ath/ath9k/debug_sta.c
index 2a3a3c4671bc..524cbf13ca9c 100644
--- a/drivers/net/wireless/ath/ath9k/debug_sta.c
+++ b/drivers/net/wireless/ath/ath9k/debug_sta.c
@@ -242,6 +242,59 @@ static const struct file_operations fops_node_recv = {
 	.llseek = default_llseek,
 };
 
+void ath_debug_airtime(struct ath_softc *sc,
+		struct ath_node *an,
+		u32 rx,
+		u32 tx)
+{
+	struct ath_airtime_stats *astats = &an->airtime_stats;
+
+	astats->rx_airtime += rx;
+	astats->tx_airtime += tx;
+}
+
+static ssize_t read_airtime(struct file *file, char __user *user_buf,
+			size_t count, loff_t *ppos)
+{
+	struct ath_node *an = file->private_data;
+	struct ath_airtime_stats *astats;
+	static const char *qname[4] = {
+		"VO", "VI", "BE", "BK"
+	};
+	u32 len = 0, size = 256;
+	char *buf;
+	size_t retval;
+	int i;
+
+	buf = kzalloc(size, GFP_KERNEL);
+	if (buf == NULL)
+		return -ENOMEM;
+
+	astats = &an->airtime_stats;
+
+	len += scnprintf(buf + len, size - len, "RX: %u us\n", astats->rx_airtime);
+	len += scnprintf(buf + len, size - len, "TX: %u us\n", astats->tx_airtime);
+	len += scnprintf(buf + len, size - len, "Deficit: ");
+	for (i = 0; i < 4; i++)
+		len += scnprintf(buf+len, size - len, "%s: %lld us ", qname[i], an->airtime_deficit[i]);
+	if (len < size)
+		buf[len++] = '\n';
+
+	retval = simple_read_from_buffer(user_buf, count, ppos, buf, len);
+	kfree(buf);
+
+	return retval;
+}
+
+
+static const struct file_operations fops_airtime = {
+	.read = read_airtime,
+	.open = simple_open,
+	.owner = THIS_MODULE,
+	.llseek = default_llseek,
+};
+
+
 void ath9k_sta_add_debugfs(struct ieee80211_hw *hw,
 			   struct ieee80211_vif *vif,
 			   struct ieee80211_sta *sta,
@@ -251,4 +304,5 @@ void ath9k_sta_add_debugfs(struct ieee80211_hw *hw,
 
 	debugfs_create_file("node_aggr", S_IRUGO, dir, an, &fops_node_aggr);
 	debugfs_create_file("node_recv", S_IRUGO, dir, an, &fops_node_recv);
+	debugfs_create_file("airtime", S_IRUGO, dir, an, &fops_airtime);
 }