mac80211: Prevent running sta_cleanup timer unnecessarily

The sta_cleanup timer is used to periodically expire buffered frames from the
tx buf. The timer is executing periodically, regardless of the need for it.
This is wasting resources.

Fix this simply by not restarting the sta_cleanup timer if the tx buffer was
empty. Restart the timer when there is some more tx-traffic.

Cc: Janne Ylälehto <janne.ylalehto@nokia.com>
Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/sta_info.c

@@ -575,7 +575,7 @@ static int sta_info_buffer_expired(struct sta_info *sta,
 }
 
 
-static void sta_info_cleanup_expire_buffered(struct ieee80211_local *local,
+static bool sta_info_cleanup_expire_buffered(struct ieee80211_local *local,
 					     struct sta_info *sta)
 {
 	unsigned long flags;
@@ -583,7 +583,7 @@ static void sta_info_cleanup_expire_buffered(struct ieee80211_local *local,
 	struct ieee80211_sub_if_data *sdata;
 
 	if (skb_queue_empty(&sta->ps_tx_buf))
-		return;
+		return false;
 
 	for (;;) {
 		spin_lock_irqsave(&sta->ps_tx_buf.lock, flags);
@@ -608,6 +608,8 @@ static void sta_info_cleanup_expire_buffered(struct ieee80211_local *local,
 		if (skb_queue_empty(&sta->ps_tx_buf))
 			sta_info_clear_tim_bit(sta);
 	}
+
+	return true;
 }
 
 static int __must_check __sta_info_destroy(struct sta_info *sta)
@@ -755,15 +757,20 @@ static void sta_info_cleanup(unsigned long data)
 {
 	struct ieee80211_local *local = (struct ieee80211_local *) data;
 	struct sta_info *sta;
+	bool timer_needed = false;
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(sta, &local->sta_list, list)
-		sta_info_cleanup_expire_buffered(local, sta);
+		if (sta_info_cleanup_expire_buffered(local, sta))
+			timer_needed = true;
 	rcu_read_unlock();
 
 	if (local->quiescing)
 		return;
 
+	if (!timer_needed)
+		return;
+
 	local->sta_cleanup.expires =
 		round_jiffies(jiffies + STA_INFO_CLEANUP_INTERVAL);
 	add_timer(&local->sta_cleanup);

net/mac80211/tx.c

@@ -429,6 +429,7 @@ ieee80211_tx_h_unicast_ps_buf(struct ieee80211_tx_data *tx)
 	struct sta_info *sta = tx->sta;
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(tx->skb);
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)tx->skb->data;
+	struct ieee80211_local *local = tx->local;
 	u32 staflags;
 
 	if (unlikely(!sta ||
@@ -476,6 +477,12 @@ ieee80211_tx_h_unicast_ps_buf(struct ieee80211_tx_data *tx)
 		info->control.vif = &tx->sdata->vif;
 		info->flags |= IEEE80211_TX_INTFL_NEED_TXPROCESSING;
 		skb_queue_tail(&sta->ps_tx_buf, tx->skb);
+
+		if (!timer_pending(&local->sta_cleanup))
+			mod_timer(&local->sta_cleanup,
+				  round_jiffies(jiffies +
+						STA_INFO_CLEANUP_INTERVAL));
+
 		return TX_QUEUED;
 	}
 #ifdef CONFIG_MAC80211_VERBOSE_PS_DEBUG