[Make-wifi-fast] [PATCH v3 4/4] mac80211: Use Airtime-based Queue Limits (AQL) on packet dequeue

[Kan Yan]

> +       if (local->airtime_flags & AIRTIME_USE_AQL) {
> +               airtime = ieee80211_calc_expected_tx_airtime(hw, vif, txq->sta,
> +                                                            skb->len);
> +               if (airtime) {
> +                       /* We only have 10 bits in tx_time_est, so store airtime
> +                        * in increments of 4 us and clamp that to 2**10.
> +                        */
> +                       info->tx_time_est = min_t(u32, airtime >> 2, 1 << 10);
> +                       ieee80211_sta_update_pending_airtime(local, tx.sta, ac,
> +                                                            airtime, false);
> +               }
> +       }
> +

It should be:
                         ieee80211_sta_update_pending_airtime(local, tx.sta, ac,

info->tx_time_est << 2, false);

The airtime rounded to 4us (info->tx_time_est << 2), instead of the
original airtime should be used when registering the pending airtime,
to keep it consistent with airtime subtracted when the skb is freed.


On Fri, Oct 18, 2019 at 7:40 AM Toke Høiland-Jørgensen <toke at redhat.com> wrote:
>
> From: Toke Høiland-Jørgensen <toke at redhat.com>
>
> The previous commit added the ability to throttle stations when they queue
> too much airtime in the hardware. This commit enables the functionality by
> calculating the expected airtime usage of each packet that is dequeued from
> the TXQs in mac80211, and accounting that as pending airtime.
>
> The estimated airtime for each skb is stored in the tx_info, so we can
> subtract the same amount from the running total when the skb is freed or
> recycled. The throttling mechanism relies on this accounting to be
> accurate (i.e., that we are not freeing skbs without subtracting any
> airtime they were accounted for), so we put the subtraction into
> ieee80211_report_used_skb(). As an optimisation, we also subtract the
> airtime on regular TX completion, zeroing out the value stored in the
> packet afterwards, to avoid having to do an expensive lookup of the
> station from the packet data on every packet.
>
> This patch does *not* include any mechanism to wake a throttled TXQ again,
> on the assumption that this will happen anyway as a side effect of whatever
> freed the skb (most commonly a TX completion).
>
> Signed-off-by: Toke Høiland-Jørgensen <toke at redhat.com>
> ---
>  net/mac80211/status.c |   38 ++++++++++++++++++++++++++++++++++++++
>  net/mac80211/tx.c     |   19 +++++++++++++++++++
>  2 files changed, 57 insertions(+)
>
> diff --git a/net/mac80211/status.c b/net/mac80211/status.c
> index ab8ba5835ca0..905b4afd457d 100644
> --- a/net/mac80211/status.c
> +++ b/net/mac80211/status.c
> @@ -676,6 +676,33 @@ static void ieee80211_report_used_skb(struct ieee80211_local *local,
>         if (dropped)
>                 acked = false;
>
> +       if (info->tx_time_est) {
> +               struct ieee80211_sub_if_data *sdata;
> +               struct sta_info *sta = NULL;
> +               u8 *qc, ac;
> +               int tid;
> +
> +               rcu_read_lock();
> +
> +               sdata = ieee80211_sdata_from_skb(local, skb);
> +               if (sdata)
> +                       sta = sta_info_get_bss(sdata, skb_mac_header(skb));
> +
> +               if (ieee80211_is_data_qos(hdr->frame_control)) {
> +                       qc = ieee80211_get_qos_ctl(hdr);
> +                       tid = qc[0] & 0xf;
> +                       ac = ieee80211_ac_from_tid(tid);
> +               } else {
> +                       ac = IEEE80211_AC_BE;
> +               }
> +
> +               ieee80211_sta_update_pending_airtime(local, sta, ac,
> +                                                    info->tx_time_est << 2,
> +                                                    true);
> +               rcu_read_unlock();
> +
> +       }
> +
>         if (info->flags & IEEE80211_TX_INTFL_MLME_CONN_TX) {
>                 struct ieee80211_sub_if_data *sdata;
>
> @@ -930,6 +957,17 @@ static void __ieee80211_tx_status(struct ieee80211_hw *hw,
>                         tid = qc[0] & 0xf;
>                 }
>
> +               if (info->tx_time_est) {
> +                       /* Do this here to avoid the expensive lookup of the sta
> +                        * in ieee80211_report_used_skb().
> +                        */
> +                       ieee80211_sta_update_pending_airtime(local, sta,
> +                                                            ieee80211_ac_from_tid(tid),
> +                                                            info->tx_time_est << 2,
> +                                                            true);
> +                       info->tx_time_est = 0;
> +               }
> +
>                 if (!acked && ieee80211_is_back_req(fc)) {
>                         u16 control;
>
> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
> index 12653d873b8c..bd8284f04361 100644
> --- a/net/mac80211/tx.c
> +++ b/net/mac80211/tx.c
> @@ -3539,9 +3539,14 @@ struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
>         struct ieee80211_tx_data tx;
>         ieee80211_tx_result r;
>         struct ieee80211_vif *vif = txq->vif;
> +       u8 ac = txq->ac;
> +       u32 airtime;
>
>         WARN_ON_ONCE(softirq_count() == 0);
>
> +       if (!ieee80211_txq_airtime_check(hw, txq))
> +               return NULL;
> +
>  begin:
>         spin_lock_bh(&fq->lock);
>
> @@ -3652,6 +3657,20 @@ struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
>         }
>
>         IEEE80211_SKB_CB(skb)->control.vif = vif;
> +
> +       if (local->airtime_flags & AIRTIME_USE_AQL) {
> +               airtime = ieee80211_calc_expected_tx_airtime(hw, vif, txq->sta,
> +                                                            skb->len);
> +               if (airtime) {
> +                       /* We only have 10 bits in tx_time_est, so store airtime
> +                        * in increments of 4 us and clamp that to 2**10.
> +                        */
> +                       info->tx_time_est = min_t(u32, airtime >> 2, 1 << 10);
> +                       ieee80211_sta_update_pending_airtime(local, tx.sta, ac,
> +                                                            airtime, false);
> +               }
> +       }
> +
>         return skb;
>
>  out:
>