[Make-wifi-fast] [PATCH RFC/RFT 4/4] mac80211: Apply Airtime-based Queue Limit (AQL) on packet dequeue

[Toke Høiland-Jørgensen]

Yibo Zhao <yiboz at codeaurora.org> writes:

> So if it is going to work together with virtual time based mechanism in 
> the future, the Tx criteria will be met both of below conditions,
>         1. Lower than g_vt
>         2. Lower than IEEE80211_AIRTIME_QUEUE_LIMIT

> Are we going to maintain two kinds of airtime that one is from 
> estimation and the other is basically from FW reporting?

Yes, that was my plan. For devices that don't have FW reporting of
airtime, we can fall back to the estimation; but if we do have FW
reporting that is most likely going to be more accurate, so better to
use that for fairness...

> Meanwhile, airtime_queued will also limit the situation that we only
> have a station for transmission. Not sure if the peak throughput will
> be impacted. I believe it may work fine with 11ac in chromiumos, how
> about 11n and 11a?

Well, we will need to test that, of course. But ath9k shows that it's
quite possible to run with quite shallow buffers, so with a bit of
tuning I think we should be fine. If anything, slower networks need
*fewer* packets queued in the firmware, and it's *easier* for the host
to keep up with transmission.

> Anyway, I think this approach will help to improve performance of the 
> virtual time based mechanism since it makes packets buffered in host 
> instead of FW's deep queue. We have observed 2-clients case with 
> different ratio in TCP fails to maintain the ratio because the packets 
> arriving at host get pushed to FW immediately and thus the airtime 
> weight sum is 0 in most of time meaning no TXQ in the rbtree. For UDP, 
> if we pump load more than the PHY rate, the ratio can be maintained 
> beacuse the FW queue is full and packtes begin to be buffered in host 
> making TXQs staying on the rbtree for most of time. However, TCP has its 
> own flow control that we can not push enough load like UDP.

Yes, fixing that is exactly the point of this series :)

-Toke