Re: [PATCH ath-next v4 7/9] wifi: ath11k: charge received airtime to the station deficit

[Tamizh Raja]

On Tue, Sep 8, 2026 at 7:23 PM Julius Bairaktaris <julius@xxxxxxxxxxxxxx> wrote:
>
> mac80211's airtime scheduler is configured to account both directions:
> local->airtime_flags is AIRTIME_USE_TX | AIRTIME_USE_RX, and
> ieee80211_sta_register_airtime() adds the received airtime to the same
> deficit the transmit side subtracts from. ath11k passes zero for it, so
> an access point serving a station that mostly uploads charges that
> station nothing for the medium it occupies, and the deficit that decides
> whose queue is served next describes half the traffic.
>
> Register the duration the hardware reports for each received PPDU. It
> arrives in the RXPCU PPDU end TLV on the monitor status ring, which is
> subscribed for every radio, and ath11k already accumulates it as the
> station's rx_duration. Charging it once per PPDU matches what the
> transmit side registers, whereas an estimate rebuilt per MSDU counts the
> preamble and the interframe space once for every subframe of an
> aggregate.
>
> The PPDU end user stats TLV that names the TID is not in the default
> monitor status filter, so the airtime is charged to best effort, the
> access category the deficit arbitrates the bulk of the traffic in. The

This means the resulting fairness accounting is only an approximation
and can leave VO/VI deficits
uncharged while accumulating all received airtime against BE

> call is made after ab->base_lock is dropped, under the rcu read lock the
> loop holds, as the tx completion path does; base_lock is contended by
> every tx completion. A PPDU from a peer with no station entry is not
> charged to anyone.
>
> Tested-on: IPQ8074 hw2.0 AHB WLAN.HK.2.9.0.1-02146-QCAHKSWPL_SILICONZ-1
>
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Julius Bairaktaris <julius@xxxxxxxxxxxxxx>
> ---
>  drivers/net/wireless/ath/ath11k/dp_rx.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/drivers/net/wireless/ath/ath11k/dp_rx.c b/drivers/net/wireless/ath/ath11k/dp_rx.c
> index 68472e1e748a..a7b9bb295728 100644
> --- a/drivers/net/wireless/ath/ath11k/dp_rx.c
> +++ b/drivers/net/wireless/ath/ath11k/dp_rx.c
> @@ -5270,6 +5270,7 @@ int ath11k_dp_rx_process_mon_status(struct ath11k_base *ab, int mac_id,
>         struct sk_buff_head skb_list;
>         struct ath11k_peer *peer;
>         struct ath11k_sta *arsta;
> +       struct ieee80211_sta *sta;
>         int num_buffs_reaped = 0;
>         u32 rx_buf_sz;
>         u16 log_type;
> @@ -5324,6 +5325,7 @@ int ath11k_dp_rx_process_mon_status(struct ath11k_base *ab, int mac_id,
>                         continue;
>                 }
>
> +               sta = NULL;
>                 rcu_read_lock();
>                 spin_lock_bh(&ab->base_lock);
>                 peer = ath11k_peer_find_by_id(ab, ppdu_info->peer_id);
> @@ -5337,12 +5339,25 @@ int ath11k_dp_rx_process_mon_status(struct ath11k_base *ab, int mac_id,
>
>                 arsta = ath11k_sta_to_arsta(peer->sta);
>                 ath11k_dp_rx_update_peer_stats(arsta, ppdu_info);
> +               sta = peer->sta;
>
>                 if (ath11k_debugfs_is_pktlog_peer_valid(ar, peer->addr))
>                         trace_ath11k_htt_rxdesc(ar, skb->data, log_type, rx_buf_sz);
>
>  next_skb:
>                 spin_unlock_bh(&ab->base_lock);
> +
> +               /* The airtime a station spends transmitting is taken from
> +                * the others, so its deficit is charged for it too, with the
> +                * duration the hardware measured for the whole PPDU, as on
> +                * the transmit side. The TLV that names the TID is not in
> +                * the default monitor status filter, so the charge goes to
> +                * BE. Outside base_lock, which tx completion contends for;
> +                * sta is held by the rcu read lock.
> +                */
> +               if (sta && ppdu_info->rx_duration)
> +                       ieee80211_sta_register_airtime(sta, 0, 0,
> +                                                      ppdu_info->rx_duration);
>                 rcu_read_unlock();
>
>                 dev_kfree_skb_any(skb);
> --
> 2.53.0
>
>


-- 
- Tamizh.