Re: [PATCH v9 3/4] mac80211: Implement Airtime-based Queue Limit (AQL)

[Kan Yan <kyan@google.com>]

> @@ -3685,13 +3686,26 @@ struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac)
>         if (!txqi)
>                 goto out;
> +       if (txqi == head && !found_eligible_txq)
> +               goto out;
> +
> +       if (!head)
> +               head = txqi;
> +
>         if (txqi->txq.sta) {
>                 struct sta_info *sta = container_of(txqi->txq.sta,
> -                                               struct sta_info, sta);
> +                                                   struct sta_info, sta);
> +               bool aql_check = ieee80211_txq_airtime_check(hw, &txqi->txq);
> +               s64 deficit = sta->airtime[txqi->txq.ac].deficit;
> +
> +               if (aql_check)
> +                       found_eligible_txq = true;
> -               if (sta->airtime[txqi->txq.ac].deficit < 0) {
> +               if (deficit < 0)
>                         sta->airtime[txqi->txq.ac].deficit +=
>                                 sta->airtime_weight;
> +
> +               if (deficit < 0 || !aql_check) {
>                         list_move_tail(&txqi->schedule_order,
>                                        &local->active_txqs[txqi->txq.ac]);
>                         goto begin;

Recent tests detect softlockup in ieee80211_next_txq(). The problem is
when a txq is deemed eligible for transmitting by
ieee80211_txq_airtime_check() but has negative deficit, the above
block keeps iterate over the list of active_txqs to refill the deficit
until it became positive. However, there could be other tx activities
for other ACs in the meantime, which increases
aql_total_pending_airtime and causes ieee80211_txq_airtime_check()
returns false and hence the lockup condition.

found_eligible_txq need be reset after each iteration of active_txqs.
I will upload a new version to fix it soon.
> @@ -3685,13 +3686,26 @@ struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac)
>         if (!txqi)
>                 goto out;
> +       if (txqi == head && !found_eligible_txq)
> +               goto out;
> +
> +       if (!head)
> +               head = txqi;
> +
>         if (txqi->txq.sta) {
>                 struct sta_info *sta = container_of(txqi->txq.sta,
> -                                               struct sta_info, sta);
> +                                                   struct sta_info, sta);
> +               bool aql_check = ieee80211_txq_airtime_check(hw, &txqi->txq);
> +               s64 deficit = sta->airtime[txqi->txq.ac].deficit;
> +
> +               if (aql_check)
> +                       found_eligible_txq = true;
> -               if (sta->airtime[txqi->txq.ac].deficit < 0) {
> +               if (deficit < 0)
>                         sta->airtime[txqi->txq.ac].deficit +=
>                                 sta->airtime_weight;
> +
> +               if (deficit < 0 || !aql_check) {
>                         list_move_tail(&txqi->schedule_order,
>                                        &local->active_txqs[txqi->txq.ac]);
>                         goto begin;


On Fri, Nov 15, 2019 at 5:20 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> From: Kan Yan <kyan@google.com>
>
> In order for the Fq_CoDel algorithm integrated in mac80211 layer to operate
> effectively to control excessive queueing latency, the CoDel algorithm
> requires an accurate measure of how long packets stays in the queue, AKA
> sojourn time. The sojourn time measured at the mac80211 layer doesn't
> include queueing latency in the lower layer (firmware/hardware) and CoDel
> expects lower layer to have a short queue. However, most 802.11ac chipsets
> offload tasks such TX aggregation to firmware or hardware, thus have a deep
> lower layer queue.
>
> Without a mechanism to control the lower layer queue size, packets only
> stay in mac80211 layer transiently before being sent to firmware queue.
> As a result, the sojourn time measured by CoDel in the mac80211 layer is
> almost always lower than the CoDel latency target, hence CoDel does little
> to control the latency, even when the lower layer queue causes excessive
> latency.
>
> The Byte Queue Limits (BQL) mechanism is commonly used to address the
> similar issue with wired network interface. However, this method cannot be
> applied directly to the wireless network interface. "Bytes" is not a
> suitable measure of queue depth in the wireless network, as the data rate
> can vary dramatically from station to station in the same network, from a
> few Mbps to over Gbps.
>
> This patch implements an Airtime-based Queue Limit (AQL) to make CoDel work
> effectively with wireless drivers that utilized firmware/hardware
> offloading. AQL allows each txq to release just enough packets to the lower
> layer to form 1-2 large aggregations to keep hardware fully utilized and
> retains the rest of the frames in mac80211 layer to be controlled by the
> CoDel algorithm.
>
> Signed-off-by: Kan Yan <kyan@google.com>
> [ Toke: Keep API to set pending airtime internal, fix nits in commit msg ]
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> ---
>  include/net/cfg80211.h     |    7 ++++
>  include/net/mac80211.h     |   12 ++++++
>  net/mac80211/debugfs.c     |   85 ++++++++++++++++++++++++++++++++++++++++++++
>  net/mac80211/debugfs_sta.c |   43 +++++++++++++++++-----
>  net/mac80211/ieee80211_i.h |    4 ++
>  net/mac80211/main.c        |   10 +++++
>  net/mac80211/sta_info.c    |   38 ++++++++++++++++++++
>  net/mac80211/sta_info.h    |    8 ++++
>  net/mac80211/tx.c          |   47 +++++++++++++++++++++++-
>  9 files changed, 240 insertions(+), 14 deletions(-)
>
> diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
> index e309cc826b40..4f75dbdd406a 100644
> --- a/include/net/cfg80211.h
> +++ b/include/net/cfg80211.h
> @@ -2606,6 +2606,13 @@ enum wiphy_params_flags {
>
>  #define IEEE80211_DEFAULT_AIRTIME_WEIGHT       256
>
> +/* The per TXQ device queue limit in airtime */
> +#define IEEE80211_DEFAULT_AQL_TXQ_LIMIT_L      4000
> +#define IEEE80211_DEFAULT_AQL_TXQ_LIMIT_H      8000
> +
> +/* The per interface airtime threshold to switch to lower queue limit */
> +#define IEEE80211_AQL_THRESHOLD                        24000
> +
>  /**
>   * struct cfg80211_pmksa - PMK Security Association
>   *
> diff --git a/include/net/mac80211.h b/include/net/mac80211.h
> index 6fc26a051ba0..ba3f33cc41ea 100644
> --- a/include/net/mac80211.h
> +++ b/include/net/mac80211.h
> @@ -5565,6 +5565,18 @@ void ieee80211_send_eosp_nullfunc(struct ieee80211_sta *pubsta, int tid);
>  void ieee80211_sta_register_airtime(struct ieee80211_sta *pubsta, u8 tid,
>                                     u32 tx_airtime, u32 rx_airtime);
>
> +/**
> + * ieee80211_txq_airtime_check - check if a txq can send frame to device
> + *
> + * @hw: pointer obtained from ieee80211_alloc_hw()
> + * @txq: pointer obtained from station or virtual interface
> + *
> + * Return true if the AQL's airtime limit has not been reached and the txq can
> + * continue to send more packets to the device. Otherwise return false.
> + */
> +bool
> +ieee80211_txq_airtime_check(struct ieee80211_hw *hw, struct ieee80211_txq *txq);
> +
>  /**
>   * ieee80211_iter_keys - iterate keys programmed into the device
>   * @hw: pointer obtained from ieee80211_alloc_hw()
> diff --git a/net/mac80211/debugfs.c b/net/mac80211/debugfs.c
> index 568b3b276931..399d4e8b8546 100644
> --- a/net/mac80211/debugfs.c
> +++ b/net/mac80211/debugfs.c
> @@ -148,6 +148,87 @@ static const struct file_operations aqm_ops = {
>         .llseek = default_llseek,
>  };
>
> +static ssize_t aql_txq_limit_read(struct file *file,
> +                                 char __user *user_buf,
> +                                 size_t count,
> +                                 loff_t *ppos)
> +{
> +       struct ieee80211_local *local = file->private_data;
> +       char buf[400];
> +       int len = 0;
> +
> +       len = scnprintf(buf, sizeof(buf),
> +                       "AC     AQL limit low   AQL limit high\n"
> +                       "VO     %u              %u\n"
> +                       "VI     %u              %u\n"
> +                       "BE     %u              %u\n"
> +                       "BK     %u              %u\n",
> +                       local->aql_txq_limit_low[IEEE80211_AC_VO],
> +                       local->aql_txq_limit_high[IEEE80211_AC_VO],
> +                       local->aql_txq_limit_low[IEEE80211_AC_VI],
> +                       local->aql_txq_limit_high[IEEE80211_AC_VI],
> +                       local->aql_txq_limit_low[IEEE80211_AC_BE],
> +                       local->aql_txq_limit_high[IEEE80211_AC_BE],
> +                       local->aql_txq_limit_low[IEEE80211_AC_BK],
> +                       local->aql_txq_limit_high[IEEE80211_AC_BK]);
> +       return simple_read_from_buffer(user_buf, count, ppos,
> +                                      buf, len);
> +}
> +
> +static ssize_t aql_txq_limit_write(struct file *file,
> +                                  const char __user *user_buf,
> +                                  size_t count,
> +                                  loff_t *ppos)
> +{
> +       struct ieee80211_local *local = file->private_data;
> +       char buf[100];
> +       size_t len;
> +       u32 ac, q_limit_low, q_limit_high, q_limit_low_old, q_limit_high_old;
> +       struct sta_info *sta;
> +
> +       if (count > sizeof(buf))
> +               return -EINVAL;
> +
> +       if (copy_from_user(buf, user_buf, count))
> +               return -EFAULT;
> +
> +       buf[sizeof(buf) - 1] = 0;
> +       len = strlen(buf);
> +       if (len > 0 && buf[len - 1] == '\n')
> +               buf[len - 1] = 0;
> +
> +       if (sscanf(buf, "%u %u %u", &ac, &q_limit_low, &q_limit_high) != 3)
> +               return -EINVAL;
> +
> +       if (ac >= IEEE80211_NUM_ACS)
> +               return -EINVAL;
> +
> +       q_limit_low_old = local->aql_txq_limit_low[ac];
> +       q_limit_high_old = local->aql_txq_limit_high[ac];
> +
> +       local->aql_txq_limit_low[ac] = q_limit_low;
> +       local->aql_txq_limit_high[ac] = q_limit_high;
> +
> +       mutex_lock(&local->sta_mtx);
> +       list_for_each_entry(sta, &local->sta_list, list) {
> +               /* If a sta has customized queue limits, keep it */
> +               if (sta->airtime[ac].aql_limit_low == q_limit_low_old &&
> +                   sta->airtime[ac].aql_limit_high == q_limit_high_old) {
> +                       sta->airtime[ac].aql_limit_low = q_limit_low;
> +                       sta->airtime[ac].aql_limit_high = q_limit_high;
> +               }
> +       }
> +       mutex_unlock(&local->sta_mtx);
> +       return count;
> +}
> +
> +static const struct file_operations aql_txq_limit_ops = {
> +       .write = aql_txq_limit_write,
> +       .read = aql_txq_limit_read,
> +       .open = simple_open,
> +       .llseek = default_llseek,
> +};
> +
>  static ssize_t force_tx_status_read(struct file *file,
>                                     char __user *user_buf,
>                                     size_t count,
> @@ -441,6 +522,10 @@ void debugfs_hw_add(struct ieee80211_local *local)
>         debugfs_create_u16("airtime_flags", 0600,
>                            phyd, &local->airtime_flags);
>
> +       DEBUGFS_ADD(aql_txq_limit);
> +       debugfs_create_u32("aql_threshold", 0600,
> +                          phyd, &local->aql_threshold);
> +
>         statsd = debugfs_create_dir("statistics", phyd);
>
>         /* if the dir failed, don't put all the other things into the root! */
> diff --git a/net/mac80211/debugfs_sta.c b/net/mac80211/debugfs_sta.c
> index c8ad20c28c43..0185e6e5e5d1 100644
> --- a/net/mac80211/debugfs_sta.c
> +++ b/net/mac80211/debugfs_sta.c
> @@ -197,10 +197,12 @@ static ssize_t sta_airtime_read(struct file *file, char __user *userbuf,
>  {
>         struct sta_info *sta = file->private_data;
>         struct ieee80211_local *local = sta->sdata->local;
> -       size_t bufsz = 200;
> +       size_t bufsz = 400;
>         char *buf = kzalloc(bufsz, GFP_KERNEL), *p = buf;
>         u64 rx_airtime = 0, tx_airtime = 0;
>         s64 deficit[IEEE80211_NUM_ACS];
> +       u32 q_depth[IEEE80211_NUM_ACS];
> +       u32 q_limit_l[IEEE80211_NUM_ACS], q_limit_h[IEEE80211_NUM_ACS];
>         ssize_t rv;
>         int ac;
>
> @@ -212,19 +214,22 @@ static ssize_t sta_airtime_read(struct file *file, char __user *userbuf,
>                 rx_airtime += sta->airtime[ac].rx_airtime;
>                 tx_airtime += sta->airtime[ac].tx_airtime;
>                 deficit[ac] = sta->airtime[ac].deficit;
> +               q_limit_l[ac] = sta->airtime[ac].aql_limit_low;
> +               q_limit_h[ac] = sta->airtime[ac].aql_limit_high;
>                 spin_unlock_bh(&local->active_txq_lock[ac]);
> +               q_depth[ac] = atomic_read(&sta->airtime[ac].aql_tx_pending);
>         }
>
>         p += scnprintf(p, bufsz + buf - p,
>                 "RX: %llu us\nTX: %llu us\nWeight: %u\n"
> -               "Deficit: VO: %lld us VI: %lld us BE: %lld us BK: %lld us\n",
> -               rx_airtime,
> -               tx_airtime,
> -               sta->airtime_weight,
> -               deficit[0],
> -               deficit[1],
> -               deficit[2],
> -               deficit[3]);
> +               "Deficit: VO: %lld us VI: %lld us BE: %lld us BK: %lld us\n"
> +               "Q depth: VO: %u us VI: %u us BE: %u us BK: %u us\n"
> +               "Q limit[low/high]: VO: %u/%u VI: %u/%u BE: %u/%u BK: %u/%u\n",
> +               rx_airtime, tx_airtime, sta->airtime_weight,
> +               deficit[0], deficit[1], deficit[2], deficit[3],
> +               q_depth[0], q_depth[1], q_depth[2], q_depth[3],
> +               q_limit_l[0], q_limit_h[0], q_limit_l[1], q_limit_h[1],
> +               q_limit_l[2], q_limit_h[2], q_limit_l[3], q_limit_h[3]),
>
>         rv = simple_read_from_buffer(userbuf, count, ppos, buf, p - buf);
>         kfree(buf);
> @@ -236,7 +241,25 @@ static ssize_t sta_airtime_write(struct file *file, const char __user *userbuf,
>  {
>         struct sta_info *sta = file->private_data;
>         struct ieee80211_local *local = sta->sdata->local;
> -       int ac;
> +       u32 ac, q_limit_l, q_limit_h;
> +       char _buf[100] = {}, *buf = _buf;
> +
> +       if (count > sizeof(_buf))
> +               return -EINVAL;
> +
> +       if (copy_from_user(buf, userbuf, count))
> +               return -EFAULT;
> +
> +       buf[sizeof(_buf) - 1] = '\0';
> +       if (sscanf(buf, "queue limit %u %u %u", &ac, &q_limit_l, &q_limit_h)
> +           != 3)
> +               return -EINVAL;
> +
> +       if (ac >= IEEE80211_NUM_ACS)
> +               return -EINVAL;
> +
> +       sta->airtime[ac].aql_limit_low = q_limit_l;
> +       sta->airtime[ac].aql_limit_high = q_limit_h;
>
>         for (ac = 0; ac < IEEE80211_NUM_ACS; ac++) {
>                 spin_lock_bh(&local->active_txq_lock[ac]);
> diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
> index 225ea4e3cd76..ad15b3be8bb3 100644
> --- a/net/mac80211/ieee80211_i.h
> +++ b/net/mac80211/ieee80211_i.h
> @@ -1142,6 +1142,10 @@ struct ieee80211_local {
>         u16 schedule_round[IEEE80211_NUM_ACS];
>
>         u16 airtime_flags;
> +       u32 aql_txq_limit_low[IEEE80211_NUM_ACS];
> +       u32 aql_txq_limit_high[IEEE80211_NUM_ACS];
> +       u32 aql_threshold;
> +       atomic_t aql_total_pending_airtime;
>
>         const struct ieee80211_ops *ops;
>
> diff --git a/net/mac80211/main.c b/net/mac80211/main.c
> index aba094b4ccfc..071ea92a3748 100644
> --- a/net/mac80211/main.c
> +++ b/net/mac80211/main.c
> @@ -667,8 +667,16 @@ struct ieee80211_hw *ieee80211_alloc_hw_nm(size_t priv_data_len,
>         for (i = 0; i < IEEE80211_NUM_ACS; i++) {
>                 INIT_LIST_HEAD(&local->active_txqs[i]);
>                 spin_lock_init(&local->active_txq_lock[i]);
> +               local->aql_txq_limit_low[i] = IEEE80211_DEFAULT_AQL_TXQ_LIMIT_L;
> +               local->aql_txq_limit_high[i] =
> +                       IEEE80211_DEFAULT_AQL_TXQ_LIMIT_H;
>         }
> -       local->airtime_flags = AIRTIME_USE_TX | AIRTIME_USE_RX;
> +
> +       local->airtime_flags = AIRTIME_USE_TX |
> +                              AIRTIME_USE_RX |
> +                              AIRTIME_USE_AQL;
> +       local->aql_threshold = IEEE80211_AQL_THRESHOLD;
> +       atomic_set(&local->aql_total_pending_airtime, 0);
>
>         INIT_LIST_HEAD(&local->chanctx_list);
>         mutex_init(&local->chanctx_mtx);
> diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
> index 465d83b13582..1fe02022a31a 100644
> --- a/net/mac80211/sta_info.c
> +++ b/net/mac80211/sta_info.c
> @@ -416,6 +416,9 @@ struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
>                 skb_queue_head_init(&sta->ps_tx_buf[i]);
>                 skb_queue_head_init(&sta->tx_filtered[i]);
>                 sta->airtime[i].deficit = sta->airtime_weight;
> +               atomic_set(&sta->airtime[i].aql_tx_pending, 0);
> +               sta->airtime[i].aql_limit_low = local->aql_txq_limit_low[i];
> +               sta->airtime[i].aql_limit_high = local->aql_txq_limit_high[i];
>         }
>
>         for (i = 0; i < IEEE80211_NUM_TIDS; i++)
> @@ -1913,6 +1916,41 @@ void ieee80211_sta_register_airtime(struct ieee80211_sta *pubsta, u8 tid,
>  }
>  EXPORT_SYMBOL(ieee80211_sta_register_airtime);
>
> +void ieee80211_sta_update_pending_airtime(struct ieee80211_local *local,
> +                                         struct sta_info *sta, u8 ac,
> +                                         u16 tx_airtime, bool tx_completed)
> +{
> +       int tx_pending;
> +
> +       if (!tx_completed) {
> +               if (sta)
> +                       atomic_add(tx_airtime,
> +                                  &sta->airtime[ac].aql_tx_pending);
> +
> +               atomic_add(tx_airtime, &local->aql_total_pending_airtime);
> +               return;
> +       }
> +
> +       if (sta) {
> +               tx_pending = atomic_sub_return(tx_airtime,
> +                                              &sta->airtime[ac].aql_tx_pending);
> +               if (WARN_ONCE(tx_pending < 0,
> +                             "STA %pM AC %d txq pending airtime underflow: %u, %u",
> +                             sta->addr, ac, tx_pending, tx_airtime))
> +                       atomic_cmpxchg(&sta->airtime[ac].aql_tx_pending,
> +                                      tx_pending, 0);
> +       }
> +
> +       tx_pending = atomic_sub_return(tx_airtime,
> +                                      &local->aql_total_pending_airtime);
> +       if (WARN_ONCE(tx_pending < 0,
> +                     "Device %s AC %d pending airtime underflow: %u, %u",
> +                     wiphy_name(local->hw.wiphy), ac, tx_pending,
> +                     tx_airtime))
> +               atomic_cmpxchg(&local->aql_total_pending_airtime,
> +                              tx_pending, 0);
> +}
> +
>  int sta_info_move_state(struct sta_info *sta,
>                         enum ieee80211_sta_state new_state)
>  {
> diff --git a/net/mac80211/sta_info.h b/net/mac80211/sta_info.h
> index 80e76569144e..0608d49b3826 100644
> --- a/net/mac80211/sta_info.h
> +++ b/net/mac80211/sta_info.h
> @@ -127,13 +127,21 @@ enum ieee80211_agg_stop_reason {
>  /* Debugfs flags to enable/disable use of RX/TX airtime in scheduler */
>  #define AIRTIME_USE_TX         BIT(0)
>  #define AIRTIME_USE_RX         BIT(1)
> +#define AIRTIME_USE_AQL                BIT(2)
>
>  struct airtime_info {
>         u64 rx_airtime;
>         u64 tx_airtime;
>         s64 deficit;
> +       atomic_t aql_tx_pending; /* Estimated airtime for frames pending */
> +       u32 aql_limit_low;
> +       u32 aql_limit_high;
>  };
>
> +void ieee80211_sta_update_pending_airtime(struct ieee80211_local *local,
> +                                         struct sta_info *sta, u8 ac,
> +                                         u16 tx_airtime, bool tx_completed);
> +
>  struct sta_info;
>
>  /**
> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
> index db38be1b75fa..aafc67b562eb 100644
> --- a/net/mac80211/tx.c
> +++ b/net/mac80211/tx.c
> @@ -3674,7 +3674,8 @@ struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac)
>  {
>         struct ieee80211_local *local = hw_to_local(hw);
>         struct ieee80211_txq *ret = NULL;
> -       struct txq_info *txqi = NULL;
> +       struct txq_info *txqi = NULL, *head = NULL;
> +       bool found_eligible_txq = false;
>
>         spin_lock_bh(&local->active_txq_lock[ac]);
>
> @@ -3685,13 +3686,26 @@ struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac)
>         if (!txqi)
>                 goto out;
>
> +       if (txqi == head && !found_eligible_txq)
> +               goto out;
> +
> +       if (!head)
> +               head = txqi;
> +
>         if (txqi->txq.sta) {
>                 struct sta_info *sta = container_of(txqi->txq.sta,
> -                                               struct sta_info, sta);
> +                                                   struct sta_info, sta);
> +               bool aql_check = ieee80211_txq_airtime_check(hw, &txqi->txq);
> +               s64 deficit = sta->airtime[txqi->txq.ac].deficit;
> +
> +               if (aql_check)
> +                       found_eligible_txq = true;
>
> -               if (sta->airtime[txqi->txq.ac].deficit < 0) {
> +               if (deficit < 0)
>                         sta->airtime[txqi->txq.ac].deficit +=
>                                 sta->airtime_weight;
> +
> +               if (deficit < 0 || !aql_check) {
>                         list_move_tail(&txqi->schedule_order,
>                                        &local->active_txqs[txqi->txq.ac]);
>                         goto begin;
> @@ -3745,6 +3759,33 @@ void __ieee80211_schedule_txq(struct ieee80211_hw *hw,
>  }
>  EXPORT_SYMBOL(__ieee80211_schedule_txq);
>
> +bool ieee80211_txq_airtime_check(struct ieee80211_hw *hw,
> +                                struct ieee80211_txq *txq)
> +{
> +       struct sta_info *sta;
> +       struct ieee80211_local *local = hw_to_local(hw);
> +
> +       if (!(local->airtime_flags & AIRTIME_USE_AQL))
> +               return true;
> +
> +       if (!txq->sta)
> +               return true;
> +
> +       sta = container_of(txq->sta, struct sta_info, sta);
> +       if (atomic_read(&sta->airtime[txq->ac].aql_tx_pending) <
> +           sta->airtime[txq->ac].aql_limit_low)
> +               return true;
> +
> +       if (atomic_read(&local->aql_total_pending_airtime) <
> +           local->aql_threshold &&
> +           atomic_read(&sta->airtime[txq->ac].aql_tx_pending) <
> +           sta->airtime[txq->ac].aql_limit_high)
> +               return true;
> +
> +       return false;
> +}
> +EXPORT_SYMBOL(ieee80211_txq_airtime_check);
> +
>  bool ieee80211_txq_may_transmit(struct ieee80211_hw *hw,
>                                 struct ieee80211_txq *txq)
>  {
>