[Make-wifi-fast] [PATCH v2 4/4] mac80211: Use Airtime-based Queue Limits (AQL) on packet dequeue

Toke Høiland-Jørgensen toke at redhat.com
Thu Oct 17 05:44:27 EDT 2019

Kan Yan <kyan at google.com> writes:

> Hi Toke,
> Thanks for getting this done! I will give it a try in the next few
> days.  A few comments:
>> 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.
> Looks like ath10k driver zero out the info->status before calling
> ieee80211_tx_status(...):
> int ath10k_txrx_tx_unref(struct ath10k_htt *htt,
>                          const struct htt_tx_done *tx_done)
> {
>  ...
>         info = IEEE80211_SKB_CB(msdu);
>         memset(&info->status, 0, sizeof(info->status));
> ...
>         ieee80211_tx_status(htt->ar->hw, msdu);
> }

Ah, bugger; I was afraid we'd run into this. A quick grep indicates that
it's only ath10k and iwl that do this, though, so it's probably
manageable to just fix this. I think the simplest solution is just to
restore the field after clearing, no?

> We need either restore the info->status.tx_time_est or calling
> ieee80211_sta_update_pending_airtime() in ath10k before tx_time_est
> get erased.
>> +       if (local->airtime_flags & AIRTIME_USE_AQL) {
>> +               airtime = ieee80211_calc_expected_tx_airtime(hw, vif, txq->sta,
>> +                                                            skb->len + 38);
> I think it is better to put the "+  38" that takes care of the header
> overhead inside ieee80211_calc_expected_tx_airtime().

Hmm, no strong opinion about this; but yeah, since we have a dedicated
function for this use I guess there's no harm in adding it there :)


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