Hi Rajkumar, It is great to see your patches and thank you for helping bring this to upstream.
> Why signed? This should never become negative unless something is wrong > with the accounting somewhere? It is signed because the "budget" is allowed to go negative. In the original version, as long as the budget is > 0, at least one packet is released even the budget is less than the airtime required for the packet. One major issue I had when doing airtime based queue limit is how to prevent txq with very low data rate (e.g., 6 mbps) from getting stalled for too long. My solution is to allow budget to go negative for one packet, then reset budget to 0 when all frames from that txq has been completed and the inflight packets count reaches to 0. For the ieee80211_calc_airtime_budget(), although it is sufficient for the purpose of enforcing queue limit, the airtime overhead estimation in the original patch really crude and could use some improvement. Instead of using the last reported tx PHY rate and a guesstimate of overhead to calculate airtime, one possible improvement is to calculate the estimated "real" tx rate from a windowed moving average of past tx_bytes/tx_airtime, if the firmware is capable of reporting tx airtime for each completed PPDU.
