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, 1 insertions, 2 deletions

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index a9b27273320e..da2447a7bade 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1118,8 +1118,7 @@ static bool ieee80211_tx_prep_agg(struct ieee80211_tx_data *tx,
 
         /* reset session timer */
         if (reset_agg_timer && tid_tx->timeout)
-                mod_timer(&tid_tx->session_timer,
-                          TU_TO_EXP_TIME(tid_tx->timeout));
+                tid_tx->last_tx = jiffies;
 
         return queued;
 }