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

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Yibo Zhao <yiboz@codeaurora.org> 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@codeaurora.org>
> Signed-off-by: Yibo Zhao <yiboz@codeaurora.org>
> Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>

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?

-Toke