Re: [PATCH 2/4] mac80211: defer txqs removal from rbtree

Yibo Zhao <yiboz@xxxxxxxxxxxxxx> · Wed, 18 Sep 2019 18:27:17 +0800

On 2019-09-18 05:10, Toke Høiland-Jørgensen wrote:
Yibo Zhao <yiboz@xxxxxxxxxxxxxx> writes:

In a loop txqs dequeue scenario, if the first txq in the rbtree gets
removed from rbtree immediately in the ieee80211_return_txq(), the
loop will break soon in the ieee80211_next_txq() due to schedule_pos
not leading to the second txq in the rbtree. Thus, defering the
removal right before the end of this schedule round.

Co-developed-by: Yibo Zhao <yiboz@xxxxxxxxxxxxxx>
Signed-off-by: Yibo Zhao <yiboz@xxxxxxxxxxxxxx>
Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxx>

I didn't write this patch, so please don't use my sign-off. I'll add
ack or review tags as appropriate in reply; but a few comments first:

---
 include/net/mac80211.h     | 16 ++++++++++--
 net/mac80211/ieee80211_i.h |  3 +++
 net/mac80211/main.c        |  6 +++++
 net/mac80211/tx.c          | 63 
+++++++++++++++++++++++++++++++++++++++++++---
 4 files changed, 83 insertions(+), 5 deletions(-)

diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index ac2ed8e..ba5a345 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -925,6 +925,8 @@ struct ieee80211_tx_rate {

 #define IEEE80211_MAX_TX_RETRY		31

+#define IEEE80211_AIRTIME_TXQ_RM_CHK_INTV_IN_MS 100
+
 static inline void ieee80211_rate_set_vht(struct ieee80211_tx_rate 
*rate,
 					  u8 mcs, u8 nss)
 {
@@ -6232,7 +6234,8 @@ struct sk_buff *ieee80211_tx_dequeue(struct 
ieee80211_hw *hw,
  * @ac: AC number to return packets from.
  *
  * Should only be called between calls to 
ieee80211_txq_schedule_start()
- * and ieee80211_txq_schedule_end().
+ * and ieee80211_txq_schedule_end(). If the txq is empty, it will be 
added
+ * to a remove list and get removed later.
  * Returns the next txq if successful, %NULL if no queue is eligible. 
If a txq
  * is returned, it should be returned with ieee80211_return_txq() 
after the
  * driver has finished scheduling it.
@@ -6268,7 +6271,8 @@ void ieee80211_txq_schedule_start(struct 
ieee80211_hw *hw, u8 ac)
  * @hw: pointer as obtained from ieee80211_alloc_hw()
  * @ac: AC number to acquire locks for
  *
- * Release locks previously acquired by ieee80211_txq_schedule_end().
+ * Release locks previously acquired by ieee80211_txq_schedule_end(). 
Check
+ * and remove the empty txq from rb-tree.
  */
 void ieee80211_txq_schedule_end(struct ieee80211_hw *hw, u8 ac)
 	__releases(txq_lock);
@@ -6287,6 +6291,14 @@ void ieee80211_schedule_txq(struct ieee80211_hw 
*hw, struct ieee80211_txq *txq)
 	__acquires(txq_lock) __releases(txq_lock);

 /**
+ * ieee80211_txqs_check - Check txqs waiting for removal
+ *
+ * @tmr: pointer as obtained from local
+ *
+ */
+void ieee80211_txqs_check(struct timer_list *tmr);
+
+/**
  * ieee80211_txq_may_transmit - check whether TXQ is allowed to 
transmit
  *
  * This function is used to check whether given txq is allowed to 
transmit by
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index a4556f9..49aa143e 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -847,6 +847,7 @@ struct txq_info {
 	struct codel_stats cstats;
 	struct sk_buff_head frags;
 	struct rb_node schedule_order;
+	struct list_head candidate;
 	unsigned long flags;

 	/* keep last! */
@@ -1145,6 +1146,8 @@ struct ieee80211_local {
 	u64 airtime_v_t[IEEE80211_NUM_ACS];
 	u64 airtime_weight_sum[IEEE80211_NUM_ACS];

+	struct list_head remove_list[IEEE80211_NUM_ACS];
+	struct timer_list remove_timer;
 	u16 airtime_flags;

 	const struct ieee80211_ops *ops;
diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index e9ffa8e..78fe24a 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -667,10 +667,15 @@ struct ieee80211_hw 
*ieee80211_alloc_hw_nm(size_t priv_data_len,

 	for (i = 0; i < IEEE80211_NUM_ACS; i++) {
 		local->active_txqs[i] = RB_ROOT_CACHED;
+		INIT_LIST_HEAD(&local->remove_list[i]);
 		spin_lock_init(&local->active_txq_lock[i]);
 	}
 	local->airtime_flags = AIRTIME_USE_TX | AIRTIME_USE_RX;

+	timer_setup(&local->remove_timer, ieee80211_txqs_check, 0);
+	mod_timer(&local->remove_timer,
+		  jiffies + 
msecs_to_jiffies(IEEE80211_AIRTIME_TXQ_RM_CHK_INTV_IN_MS));
+
 	INIT_LIST_HEAD(&local->chanctx_list);
 	mutex_init(&local->chanctx_mtx);

@@ -1305,6 +1310,7 @@ void ieee80211_unregister_hw(struct ieee80211_hw 
*hw)
 	tasklet_kill(&local->tx_pending_tasklet);
 	tasklet_kill(&local->tasklet);

+	del_timer_sync(&local->remove_timer);
 #ifdef CONFIG_INET
 	unregister_inetaddr_notifier(&local->ifa_notifier);
 #endif
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index d00baaa..42ca010 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1450,6 +1450,7 @@ void ieee80211_txq_init(struct 
ieee80211_sub_if_data *sdata,
 	codel_stats_init(&txqi->cstats);
 	__skb_queue_head_init(&txqi->frags);
 	RB_CLEAR_NODE(&txqi->schedule_order);
+	INIT_LIST_HEAD(&txqi->candidate);

 	txqi->txq.vif = &sdata->vif;

@@ -3724,6 +3725,9 @@ void ieee80211_schedule_txq(struct ieee80211_hw 
*hw,

 	spin_lock_bh(&local->active_txq_lock[ac]);

+	if (!list_empty(&txqi->candidate))
+		list_del_init(&txqi->candidate);
+
 	if (!RB_EMPTY_NODE(&txqi->schedule_order))
 		goto out;

@@ -3783,6 +3787,20 @@ static void __ieee80211_unschedule_txq(struct 
ieee80211_hw *hw,
 	RB_CLEAR_NODE(&txqi->schedule_order);
 }

+void ieee80211_remove_txq(struct ieee80211_hw *hw,
+			  struct ieee80211_txq *txq)
+{
+	struct ieee80211_local *local = hw_to_local(hw);
+	struct txq_info *txqi = to_txq_info(txq);
+
+	lockdep_assert_held(&local->active_txq_lock[txq->ac]);
+
+	if (!RB_EMPTY_NODE(&txqi->schedule_order)) {
+		__ieee80211_unschedule_txq(hw, txq);
+		list_del_init(&txqi->candidate);
+	}
+}
+
 void ieee80211_unschedule_txq(struct ieee80211_hw *hw,
 			      struct ieee80211_txq *txq)
 	__acquires(txq_lock) __releases(txq_lock)
@@ -3790,7 +3808,7 @@ void ieee80211_unschedule_txq(struct 
ieee80211_hw *hw,
 	struct ieee80211_local *local = hw_to_local(hw);

 	spin_lock_bh(&local->active_txq_lock[txq->ac]);
-	__ieee80211_unschedule_txq(hw, txq);
+	ieee80211_remove_txq(hw, txq);
 	spin_unlock_bh(&local->active_txq_lock[txq->ac]);
 }

@@ -3803,11 +3821,48 @@ void ieee80211_return_txq(struct ieee80211_hw 
*hw,
 	lockdep_assert_held(&local->active_txq_lock[txq->ac]);

 	if (!RB_EMPTY_NODE(&txqi->schedule_order) &&
-	    (skb_queue_empty(&txqi->frags) && !txqi->tin.backlog_packets))
-		__ieee80211_unschedule_txq(hw, txq);
+		!txq_has_queue(&txqi->txq) &&
+		list_empty(&txqi->candidate))
+		list_add_tail(&txqi->candidate, &local->remove_list[txq->ac]);
+
 }
 EXPORT_SYMBOL(ieee80211_return_txq);

+void __ieee80211_check_txqs(struct ieee80211_local *local, int ac)
+{
+	struct txq_info *iter, *tmp;
+	struct sta_info *sta;
+
+	lockdep_assert_held(&local->active_txq_lock[ac]);
+
+	list_for_each_entry_safe(iter, tmp, &local->remove_list[ac],
+				 candidate) {
+		sta = container_of(iter->txq.sta, struct sta_info, sta);
+
+		if (txq_has_queue(&iter->txq))
+			list_del_init(&iter->candidate);
+		else
+			ieee80211_remove_txq(&local->hw, &iter->txq);
+	}
+}
+
+void ieee80211_txqs_check(struct timer_list *t)
+{
+	struct ieee80211_local *local = from_timer(local, t, remove_timer);
+	struct txq_info *iter, *tmp;
+	struct sta_info *sta;
+	int ac;
+
+	for (ac = 0; ac < IEEE80211_NUM_ACS; ac++) {
+		spin_lock_bh(&local->active_txq_lock[ac]);
+		__ieee80211_check_txqs(local, ac);
+		spin_unlock_bh(&local->active_txq_lock[ac]);
+	}
+
+	mod_timer(&local->remove_timer,
+		  jiffies + 
msecs_to_jiffies(IEEE80211_AIRTIME_TXQ_RM_CHK_INTV_IN_MS));
+}

I'll ask the same as I did last time (where you told me to hold off
until this round):

Why do you need the timer and the periodic check? If TXQs are added to
the remove list during the scheduling run, and __ieee80211_check_txqs()
is run from schedule_end(), isn't that sufficient to clear the list?
Is it possible that a txq is not added to the remove list but then 
packets in it are dropped by fq_codel algo? Like the station disconnects 
without any notification.


-Toke

--
Yibo






