package/kernel/mac80211/patches/subsys/352-mac80211-rework-locking-for-txq-scheduling-airtime-f.patch

   1 From: Felix Fietkau <nbd@nbd.name>
   2 Date: Wed, 13 Mar 2019 19:09:22 +0100
   3 Subject: [PATCH] mac80211: rework locking for txq scheduling / airtime
   4  fairness
   5
   6 Holding the lock around the entire duration of tx scheduling can create
   7 some nasty lock contention, especially when processing airtime information
   8 from the tx status or the rx path.
   9 Improve locking by only holding the active_txq_lock for lookups / scheduling
  10 list modifications.
  11
  12 Signed-off-by: Felix Fietkau <nbd@nbd.name>
  13 ---
  14
  15 --- a/include/net/mac80211.h
  16 +++ b/include/net/mac80211.h
  17 @@ -6069,8 +6069,6 @@ struct sk_buff *ieee80211_tx_dequeue(str
  18   * @hw: pointer as obtained from ieee80211_alloc_hw()
  19   * @ac: AC number to return packets from.
  20   *
  21 - * Should only be called between calls to ieee80211_txq_schedule_start()
  22 - * and ieee80211_txq_schedule_end().
  23   * Returns the next txq if successful, %NULL if no queue is eligible. If a txq
  24   * is returned, it should be returned with ieee80211_return_txq() after the
  25   * driver has finished scheduling it.
  26 @@ -6078,51 +6076,41 @@ struct sk_buff *ieee80211_tx_dequeue(str
  27  struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac);
  28
  29  /**
  30 - * ieee80211_return_txq - return a TXQ previously acquired by ieee80211_next_txq()
  31 - *
  32 - * @hw: pointer as obtained from ieee80211_alloc_hw()
  33 - * @txq: pointer obtained from station or virtual interface
  34 - *
  35 - * Should only be called between calls to ieee80211_txq_schedule_start()
  36 - * and ieee80211_txq_schedule_end().
  37 - */
  38 -void ieee80211_return_txq(struct ieee80211_hw *hw, struct ieee80211_txq *txq);
  39 -
  40 -/**
  41 - * ieee80211_txq_schedule_start - acquire locks for safe scheduling of an AC
  42 + * ieee80211_txq_schedule_start - start new scheduling round for TXQs
  43   *
  44   * @hw: pointer as obtained from ieee80211_alloc_hw()
  45   * @ac: AC number to acquire locks for
  46   *
  47 - * Acquire locks needed to schedule TXQs from the given AC. Should be called
  48 - * before ieee80211_next_txq() or ieee80211_return_txq().
  49 + * Should be called before ieee80211_next_txq() or ieee80211_return_txq().
  50   */
  51 -void ieee80211_txq_schedule_start(struct ieee80211_hw *hw, u8 ac)
  52 -       __acquires(txq_lock);
  53 +void ieee80211_txq_schedule_start(struct ieee80211_hw *hw, u8 ac);
  54 +
  55 +/* (deprecated) */
  56 +static inline void ieee80211_txq_schedule_end(struct ieee80211_hw *hw, u8 ac)
  57 +{
  58 +}
  59
  60  /**
  61 - * ieee80211_txq_schedule_end - release locks for safe scheduling of an AC
  62 + * ieee80211_schedule_txq - schedule a TXQ for transmission
  63   *
  64   * @hw: pointer as obtained from ieee80211_alloc_hw()
  65 - * @ac: AC number to acquire locks for
  66 + * @txq: pointer obtained from station or virtual interface
  67   *
  68 - * Release locks previously acquired by ieee80211_txq_schedule_end().
  69 + * Schedules a TXQ for transmission if it is not already scheduled.
  70   */
  71 -void ieee80211_txq_schedule_end(struct ieee80211_hw *hw, u8 ac)
  72 -       __releases(txq_lock);
  73 +void ieee80211_schedule_txq(struct ieee80211_hw *hw, struct ieee80211_txq *txq);
  74
  75  /**
  76 - * ieee80211_schedule_txq - schedule a TXQ for transmission
  77 + * ieee80211_return_txq - return a TXQ previously acquired by ieee80211_next_txq()
  78   *
  79   * @hw: pointer as obtained from ieee80211_alloc_hw()
  80   * @txq: pointer obtained from station or virtual interface
  81 - *
  82 - * Schedules a TXQ for transmission if it is not already scheduled. Takes a
  83 - * lock, which means it must *not* be called between
  84 - * ieee80211_txq_schedule_start() and ieee80211_txq_schedule_end()
  85   */
  86 -void ieee80211_schedule_txq(struct ieee80211_hw *hw, struct ieee80211_txq *txq)
  87 -       __acquires(txq_lock) __releases(txq_lock);
  88 +static inline void
  89 +ieee80211_return_txq(struct ieee80211_hw *hw, struct ieee80211_txq *txq)
  90 +{
  91 +       ieee80211_schedule_txq(hw, txq);
  92 +}
  93
  94  /**
  95   * ieee80211_txq_may_transmit - check whether TXQ is allowed to transmit
  96 --- a/net/mac80211/tx.c
  97 +++ b/net/mac80211/tx.c
  98 @@ -3619,16 +3619,17 @@ EXPORT_SYMBOL(ieee80211_tx_dequeue);
  99  struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac)
 100  {
 101         struct ieee80211_local *local = hw_to_local(hw);
 102 +       struct ieee80211_txq *ret = NULL;
 103         struct txq_info *txqi = NULL;
 104
 105 -       lockdep_assert_held(&local->active_txq_lock[ac]);
 106 +       spin_lock_bh(&local->active_txq_lock[ac]);
 107
 108   begin:
 109         txqi = list_first_entry_or_null(&local->active_txqs[ac],
 110                                         struct txq_info,
 111                                         schedule_order);
 112         if (!txqi)
 113 -               return NULL;
 114 +               goto out;
 115
 116         if (txqi->txq.sta) {
 117                 struct sta_info *sta = container_of(txqi->txq.sta,
 118 @@ -3645,21 +3646,25 @@ struct ieee80211_txq *ieee80211_next_txq
 119
 120
 121         if (txqi->schedule_round == local->schedule_round[ac])
 122 -               return NULL;
 123 +               goto out;
 124
 125         list_del_init(&txqi->schedule_order);
 126         txqi->schedule_round = local->schedule_round[ac];
 127 -       return &txqi->txq;
 128 +       ret = &txqi->txq;
 129 +
 130 +out:
 131 +       spin_unlock_bh(&local->active_txq_lock[ac]);
 132 +       return ret;
 133  }
 134  EXPORT_SYMBOL(ieee80211_next_txq);
 135
 136 -void ieee80211_return_txq(struct ieee80211_hw *hw,
 137 -                         struct ieee80211_txq *txq)
 138 +void ieee80211_schedule_txq(struct ieee80211_hw *hw,
 139 +                           struct ieee80211_txq *txq)
 140  {
 141         struct ieee80211_local *local = hw_to_local(hw);
 142         struct txq_info *txqi = to_txq_info(txq);
 143
 144 -       lockdep_assert_held(&local->active_txq_lock[txq->ac]);
 145 +       spin_lock_bh(&local->active_txq_lock[txq->ac]);
 146
 147         if (list_empty(&txqi->schedule_order) &&
 148             (!skb_queue_empty(&txqi->frags) || txqi->tin.backlog_packets)) {
 149 @@ -3679,18 +3684,7 @@ void ieee80211_return_txq(struct ieee802
 150                         list_add_tail(&txqi->schedule_order,
 151                                       &local->active_txqs[txq->ac]);
 152         }
 153 -}
 154 -EXPORT_SYMBOL(ieee80211_return_txq);
 155
 156 -void ieee80211_schedule_txq(struct ieee80211_hw *hw,
 157 -                           struct ieee80211_txq *txq)
 158 -       __acquires(txq_lock) __releases(txq_lock)
 159 -{
 160 -       struct ieee80211_local *local = hw_to_local(hw);
 161 -       struct txq_info *txqi = to_txq_info(txq);
 162 -
 163 -       spin_lock_bh(&local->active_txq_lock[txq->ac]);
 164 -       ieee80211_return_txq(hw, txq);
 165         spin_unlock_bh(&local->active_txq_lock[txq->ac]);
 166  }
 167  EXPORT_SYMBOL(ieee80211_schedule_txq);
 168 @@ -3703,7 +3697,7 @@ bool ieee80211_txq_may_transmit(struct i
 169         struct sta_info *sta;
 170         u8 ac = txq->ac;
 171
 172 -       lockdep_assert_held(&local->active_txq_lock[ac]);
 173 +       spin_lock_bh(&local->active_txq_lock[ac]);
 174
 175         if (!txqi->txq.sta)
 176                 goto out;
 177 @@ -3733,34 +3727,27 @@ bool ieee80211_txq_may_transmit(struct i
 178
 179         sta->airtime[ac].deficit += sta->airtime_weight;
 180         list_move_tail(&txqi->schedule_order, &local->active_txqs[ac]);
 181 +       spin_unlock_bh(&local->active_txq_lock[ac]);
 182
 183         return false;
 184  out:
 185         if (!list_empty(&txqi->schedule_order))
 186                 list_del_init(&txqi->schedule_order);
 187 +       spin_unlock_bh(&local->active_txq_lock[ac]);
 188
 189         return true;
 190  }
 191  EXPORT_SYMBOL(ieee80211_txq_may_transmit);
 192
 193  void ieee80211_txq_schedule_start(struct ieee80211_hw *hw, u8 ac)
 194 -       __acquires(txq_lock)
 195  {
 196         struct ieee80211_local *local = hw_to_local(hw);
 197
 198         spin_lock_bh(&local->active_txq_lock[ac]);
 199         local->schedule_round[ac]++;
 200 -}
 201 -EXPORT_SYMBOL(ieee80211_txq_schedule_start);
 202 -
 203 -void ieee80211_txq_schedule_end(struct ieee80211_hw *hw, u8 ac)
 204 -       __releases(txq_lock)
 205 -{
 206 -       struct ieee80211_local *local = hw_to_local(hw);
 207 -
 208         spin_unlock_bh(&local->active_txq_lock[ac]);
 209  }
 210 -EXPORT_SYMBOL(ieee80211_txq_schedule_end);
 211 +EXPORT_SYMBOL(ieee80211_txq_schedule_start);
 212
 213  void __ieee80211_subif_start_xmit(struct sk_buff *skb,
 214                                   struct net_device *dev,