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

[Sebastian Moeller <moeller0@gmx.de>]

> On Oct 17, 2019, at 11:44, Toke Høiland-Jørgensen <toke@redhat.com> wrote:
> 
> Kan Yan <kyan@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 :)
> 

Silly question, is this Overhead guaranteed to be 38 Bytes for all eternity? Otherwise a variable or a preprocessor constant might be more future proof?

Best Regards
	Sebastian


> -Toke
> 
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