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   1 From: Felix Fietkau <nbd@nbd.name>
   2 Date: Mon, 20 Jun 2022 21:26:34 +0200
   3 Subject: [PATCH] mac80211: add a per-PHY AQL limit to improve fairness
   4
   5 In order to maintain fairness, the amount of queueing needs to be limited
   6 beyond the simple per-station AQL budget, otherwise the driver can simply
   7 repeatedly do scheduling rounds until all queues that have not used their
   8 AQL budget become eligble.
   9
  10 To be conservative, use the high AQL limit for the first txq and add half
  11 of the low AQL for each subsequent queue.
  12
  13 Signed-off-by: Felix Fietkau <nbd@nbd.name>
  14 ---
  15
  16 --- a/net/mac80211/ieee80211_i.h
  17 +++ b/net/mac80211/ieee80211_i.h
  18 @@ -1216,6 +1216,7 @@ struct ieee80211_local {
  19         u32 aql_txq_limit_high[IEEE80211_NUM_ACS];
  20         u32 aql_threshold;
  21         atomic_t aql_total_pending_airtime;
  22 +       atomic_t aql_ac_pending_airtime[IEEE80211_NUM_ACS];
  23
  24         const struct ieee80211_ops *ops;
  25
  26 --- a/net/mac80211/main.c
  27 +++ b/net/mac80211/main.c
  28 @@ -712,6 +712,7 @@ struct ieee80211_hw *ieee80211_alloc_hw_
  29                 local->aql_txq_limit_low[i] = IEEE80211_DEFAULT_AQL_TXQ_LIMIT_L;
  30                 local->aql_txq_limit_high[i] =
  31                         IEEE80211_DEFAULT_AQL_TXQ_LIMIT_H;
  32 +               atomic_set(&local->aql_ac_pending_airtime[i], 0);
  33         }
  34
  35         local->airtime_flags = AIRTIME_USE_TX | AIRTIME_USE_RX;
  36 --- a/net/mac80211/sta_info.c
  37 +++ b/net/mac80211/sta_info.c
  38 @@ -1929,6 +1929,7 @@ void ieee80211_sta_update_pending_airtim
  39                                    &sta->airtime[ac].aql_tx_pending);
  40
  41                 atomic_add(tx_airtime, &local->aql_total_pending_airtime);
  42 +               atomic_add(tx_airtime, &local->aql_ac_pending_airtime[ac]);
  43                 return;
  44         }
  45
  46 @@ -1940,14 +1941,17 @@ void ieee80211_sta_update_pending_airtim
  47                                        tx_pending, 0);
  48         }
  49
  50 +       atomic_sub(tx_airtime, &local->aql_total_pending_airtime);
  51         tx_pending = atomic_sub_return(tx_airtime,
  52 -                                      &local->aql_total_pending_airtime);
  53 +                                      &local->aql_ac_pending_airtime[ac]);
  54         if (WARN_ONCE(tx_pending < 0,
  55                       "Device %s AC %d pending airtime underflow: %u, %u",
  56                       wiphy_name(local->hw.wiphy), ac, tx_pending,
  57 -                     tx_airtime))
  58 -               atomic_cmpxchg(&local->aql_total_pending_airtime,
  59 +                     tx_airtime)) {
  60 +               atomic_cmpxchg(&local->aql_ac_pending_airtime[ac],
  61                                tx_pending, 0);
  62 +               atomic_sub(tx_pending, &local->aql_total_pending_airtime);
  63 +       }
  64  }
  65
  66  int sta_info_move_state(struct sta_info *sta,
  67 --- a/net/mac80211/tx.c
  68 +++ b/net/mac80211/tx.c
  69 @@ -3863,6 +3863,9 @@ struct ieee80211_txq *ieee80211_next_txq
  70
  71         spin_lock_bh(&local->active_txq_lock[ac]);
  72
  73 +       if (!local->schedule_round[ac])
  74 +               goto out;
  75 +
  76   begin:
  77         txqi = list_first_entry_or_null(&local->active_txqs[ac],
  78                                         struct txq_info,
  79 @@ -3984,6 +3987,25 @@ bool ieee80211_txq_airtime_check(struct
  80  }
  81  EXPORT_SYMBOL(ieee80211_txq_airtime_check);
  82
  83 +static bool
  84 +ieee80211_txq_schedule_airtime_check(struct ieee80211_local *local, u8 ac)
  85 +{
  86 +       unsigned int num_txq = 0;
  87 +       struct txq_info *txq;
  88 +       u32 aql_limit;
  89 +
  90 +       if (!wiphy_ext_feature_isset(local->hw.wiphy, NL80211_EXT_FEATURE_AQL))
  91 +               return true;
  92 +
  93 +       list_for_each_entry(txq, &local->active_txqs[ac], schedule_order)
  94 +               num_txq++;
  95 +
  96 +       aql_limit = (num_txq - 1) * local->aql_txq_limit_low[ac] / 2 +
  97 +                   local->aql_txq_limit_high[ac];
  98 +
  99 +       return atomic_read(&local->aql_ac_pending_airtime[ac]) < aql_limit;
 100 +}
 101 +
 102  bool ieee80211_txq_may_transmit(struct ieee80211_hw *hw,
 103                                 struct ieee80211_txq *txq)
 104  {
 105 @@ -4000,6 +4022,9 @@ bool ieee80211_txq_may_transmit(struct i
 106         if (list_empty(&txqi->schedule_order))
 107                 goto out;
 108
 109 +       if (!ieee80211_txq_schedule_airtime_check(local, ac))
 110 +               goto out;
 111 +
 112         list_for_each_entry_safe(iter, tmp, &local->active_txqs[ac],
 113                                  schedule_order) {
 114                 if (iter == txqi)
 115 @@ -4039,7 +4064,15 @@ void ieee80211_txq_schedule_start(struct
 116         struct ieee80211_local *local = hw_to_local(hw);
 117
 118         spin_lock_bh(&local->active_txq_lock[ac]);
 119 -       local->schedule_round[ac]++;
 120 +
 121 +       if (ieee80211_txq_schedule_airtime_check(local, ac)) {
 122 +               local->schedule_round[ac]++;
 123 +               if (!local->schedule_round[ac])
 124 +                       local->schedule_round[ac]++;
 125 +       } else {
 126 +               local->schedule_round[ac] = 0;
 127 +       }
 128 +
 129         spin_unlock_bh(&local->active_txq_lock[ac]);
 130  }
 131  EXPORT_SYMBOL(ieee80211_txq_schedule_start);