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ath9k: Measure per-station airtime usage

RFC In review Toke Høiland-Jørgensen 2 participants 3 messages May 26, 2016 – May 30, 2016 Qualcomm Atheros ATH9K wireless driver

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Toke Høiland-Jørgensen

author maintainer
#0 lore raw

RFC 1/1 ath9k: Measure per-station airtime usage

This is my attempt to add per-station airtime usage accounting to ath9k. For now I just export it to a new debugfs entry, but my plan is to use it to make (station) scheduling decisions. However, before attempting that I would like some feedback from someone more familiar with the ath9k than me as to whether this way of measuring airtime usage is likely to give reasonable results.

I realise that there's probably some things I'm missing, but an initial test run indicates that the values are at least in the right ballpark (I get a total of ~170k usecs of measured airtime per 200 ms sampling interval when running three simultaneous TCP streams to three different stations).

So can anyone comment on whether I'm on the right track here? And possibly provide some more detail as to what I'm missing and how to remedy that?

Many thanks in advance,

-Toke

---

drivers/net/wireless/ath/ath9k/ath9k.h +3 -0
index 5294595..a45faa3 100644
@@ -264,6 +264,7 @@ struct ath_node {
 
 #ifdef CONFIG_ATH9K_STATION_STATISTICS
 	struct ath_rx_rate_stats rx_rate_stats;
+	struct ath_airtime_stats airtime_stats;
 #endif
 	u8 key_idx[4];
 

@@ -564,6 +565,8 @@ void ath_txq_schedule_all(struct ath_softc *sc);
 int ath_tx_init(struct ath_softc *sc, int nbufs);
 int ath_txq_update(struct ath_softc *sc, int qnum,
 		   struct ath9k_tx_queue_info *q);
+u32 ath_pkt_duration(struct ath_softc *sc, u8 rix, int pktlen,
+		     int width, int half_gi, bool shortPreamble);
 void ath_update_max_aggr_framelen(struct ath_softc *sc, int queue, int txop);
 void ath_assign_seq(struct ath_common *common, struct sk_buff *skb);
 int ath_tx_start(struct ieee80211_hw *hw, struct sk_buff *skb,
drivers/net/wireless/ath/ath9k/debug.h +21 -0
index cd68c5f..002738e 100644
@@ -223,6 +223,11 @@ struct ath_rx_rate_stats {
 	} cck_stats[4];
 };
 
+struct ath_airtime_stats {
+	u32 rx_airtime;
+	u32 tx_airtime;
+};
+
 #define ANT_MAIN 0
 #define ANT_ALT  1
 

@@ -316,12 +321,28 @@ ath9k_debug_sync_cause(struct ath_softc *sc, u32 sync_cause)
 void ath_debug_rate_stats(struct ath_softc *sc,
 			  struct ath_rx_status *rs,
 			  struct sk_buff *skb);
+void ath_debug_tx_airtime(struct ath_softc *sc,
+		          struct ath_node *an,
+			  struct ath_tx_status *ts);
+void ath_debug_rx_airtime(struct ath_softc *sc,
+			  struct ath_rx_status *rs,
+			  struct sk_buff *skb);
 #else
 static inline void ath_debug_rate_stats(struct ath_softc *sc,
 					struct ath_rx_status *rs,
 					struct sk_buff *skb)
 {
 }
+static inline void ath_debug_tx_airtime(struct ath_softc *sc,
+					struct ath_node *an,
+					struct ath_tx_status *ts)
+{
+}
+static inline void ath_debug_rx_airtime(struct ath_softc *sc,
+					struct ath_rx_status *rs,
+					struct sk_buff *skb)
+{
+}
 #endif /* CONFIG_ATH9K_STATION_STATISTICS */
 
 #endif /* DEBUG_H */
drivers/net/wireless/ath/ath9k/debug_sta.c +102 -0

112 lines not on this page · raw message

drivers/net/wireless/ath/ath9k/recv.c +1 -0
index 32160fc..7eb8980 100644
@@ -1137,6 +1137,7 @@ 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_debug_rx_airtime(sc, &rs, skb);
 
 		hdr = (struct ieee80211_hdr *)skb->data;
 		if (ieee80211_is_ack(hdr->frame_control))
drivers/net/wireless/ath/ath9k/xmit.c +3 -2
index fe795fc..6c7304b 100644
@@ -481,6 +481,7 @@ static void ath_tx_complete_aggr(struct ath_softc *sc, struct ath_txq *txq,
 	}
 
 	an = (struct ath_node *)sta->drv_priv;
+	ath_debug_tx_airtime(sc, an, ts);
 	tid = ath_get_skb_tid(sc, an, skb);
 	seq_first = tid->seq_start;
 	isba = ts->ts_flags & ATH9K_TX_BA;

@@ -1024,8 +1025,8 @@ ath_tx_form_aggr(struct ath_softc *sc, struct ath_txq *txq,
  * width  - 0 for 20 MHz, 1 for 40 MHz
  * half_gi - to use 4us v/s 3.6 us for symbol time
  */
-static u32 ath_pkt_duration(struct ath_softc *sc, u8 rix, int pktlen,
-			    int width, int half_gi, bool shortPreamble)
+u32 ath_pkt_duration(struct ath_softc *sc, u8 rix, int pktlen,
+		     int width, int half_gi, bool shortPreamble)
 {
 	u32 nbits, nsymbits, duration, nsymbols;
 	int streams;
#1 lore raw
Quoted 16 lines · Toke H?iland-J?rgensen

This is my attempt to add per-station airtime usage accounting to ath9k. For now I just export it to a new debugfs entry, but my plan is to use it to make (station) scheduling decisions. However, before attempting that I would like some feedback from someone more familiar with the ath9k than me as to whether this way of measuring airtime usage is likely to give reasonable results.

I realise that there's probably some things I'm missing, but an initial test run indicates that the values are at least in the right ballpark (I get a total of ~170k usecs of measured airtime per 200 ms sampling interval when running three simultaneous TCP streams to three different stations).

So can anyone comment on whether I'm on the right track here? And possibly provide some more detail as to what I'm missing and how to remedy that?

[...]

drivers/net/wireless/ath/ath9k/debug_sta.c static const struct file_operations fops_node_recv = { · line 254

Quoted 11 lines
drivers/net/wireless/ath/ath9k/debug_sta.c +10 -0
+void ath_debug_tx_airtime(struct ath_softc *sc,
+                         struct ath_node *an,
+                         struct ath_tx_status *ts)
+{
+       struct ath_airtime_stats *astats;
+
+       rcu_read_lock();
+
+       astats = &an->airtime_stats;
+       astats->tx_airtime += ts->duration;

I'm not ath9k expert but this seems to be oblivious to tx retries. The ts->duration is acquired from the last used tx rate for given frame. Or am I missing something?

I think you should use ts->ts_rateindex and ts->ts_longretry to factor in retries (see ath_tx_rc_status).

Micha?

author maintainer
#2 lore raw
Quoted 6 lines · Michal Kazior
Quoted 6 lines
drivers/net/wireless/ath/ath9k/debug_sta.c +6 -0
+void ath_debug_tx_airtime(struct ath_softc *sc,
+                         struct ath_node *an,
+                         struct ath_tx_status *ts)
+{
+       struct ath_airtime_stats *astats;
+
Quoted 8 lines

drivers/net/wireless/ath/ath9k/debug_sta.c static const struct file_operations fops_node_recv = { · line 254

Quoted 4 lines
drivers/net/wireless/ath/ath9k/debug_sta.c +4 -0
+       rcu_read_lock();
+
+       astats = &an->airtime_stats;
+       astats->tx_airtime += ts->duration;

I'm not ath9k expert but this seems to be oblivious to tx retries. The ts->duration is acquired from the last used tx rate for given frame. Or am I missing something?

No, don't think you are. Wasn't sure what exactly that duration field included, but I think you're right that it doesn't factor in retries.

Quoted 2 lines

I think you should use ts->ts_rateindex and ts->ts_longretry to factor in retries (see ath_tx_rc_status).

I'll go digging. Thanks, this was exactly the kind of feedback I had hoped for! :)

-Toke