mac80211: optimize aggregation session timeout handling

Calling mod_timer from the rx/tx hotpath is somewhat expensive, and the
timeout doesn't need to be so precise.

Switch to a different strategy: Schedule the timer initially, store jiffies
of all last rx/tx activity which would previously modify the timer, and
let the timer re-arm itself after checking the last rx/tx timestamp.
Make the session timers deferrable to avoid causing extra wakeups on systems
running on battery.
This visibly reduces CPU load under high network load on small embedded
systems.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 16 insertions, 2 deletions

diff --git a/net/mac80211/agg-rx.c b/net/mac80211/agg-rx.c
index 64d3ce5ea1a..a070d4f460e 100644
--- a/net/mac80211/agg-rx.c
+++ b/net/mac80211/agg-rx.c
@@ -142,6 +142,18 @@ static void sta_rx_agg_session_timer_expired(unsigned long data)
         u8 *timer_to_id = ptid - *ptid;
         struct sta_info *sta = container_of(timer_to_id, struct sta_info,
                                          timer_to_tid[0]);
+        struct tid_ampdu_rx *tid_rx;
+        unsigned long timeout;
+
+        tid_rx = rcu_dereference(sta->ampdu_mlme.tid_rx[*ptid]);
+        if (!tid_rx)
+                return;
+
+        timeout = tid_rx->last_rx + TU_TO_JIFFIES(tid_rx->timeout);
+        if (time_is_after_jiffies(timeout)) {
+                mod_timer(&tid_rx->session_timer, timeout);
+                return;
+        }
 
 #ifdef CONFIG_MAC80211_HT_DEBUG
         printk(KERN_DEBUG "rx session timer expired on tid %d\n", (u16)*ptid);
@@ -291,7 +303,7 @@ void ieee80211_process_addba_request(struct ieee80211_local *local,
         /* rx timer */
         tid_agg_rx->session_timer.function = sta_rx_agg_session_timer_expired;
         tid_agg_rx->session_timer.data = (unsigned long)&sta->timer_to_tid[tid];
-        init_timer(&tid_agg_rx->session_timer);
+        init_timer_deferrable(&tid_agg_rx->session_timer);
 
         /* rx reorder timer */
         tid_agg_rx->reorder_timer.function = sta_rx_agg_reorder_timer_expired;
@@ -335,8 +347,10 @@ void ieee80211_process_addba_request(struct ieee80211_local *local,
         /* activate it for RX */
         rcu_assign_pointer(sta->ampdu_mlme.tid_rx[tid], tid_agg_rx);
 
-        if (timeout)
+        if (timeout) {
                 mod_timer(&tid_agg_rx->session_timer, TU_TO_EXP_TIME(timeout));
+                tid_agg_rx->last_rx = jiffies;
+        }
 
 end:
         mutex_unlock(&sta->ampdu_mlme.mtx);