[Make-wifi-fast] [PATCH v3 1/2] mac80211: Implement Airtime-based Queue Limit (AQL)

[Rich Brown]

I have been bothered by small ambiguities in the comments below. (I assume underlying code is correct.)

I have tweaked the text below to make it a bit more clear. Please feel free to correct it if I've missed what's really happening. (And please forgive my pseudo-patch code - I hope you can see the changes I am suggesting.)

Thank you all for this great work making Wi-Fi Fast!

Rich


  - In order for the Fq_CoDel integrated in mac80211 layer operates effectively
  + In order for the Fq_CoDel algorithm integrated into the mac80211 layer
	to control excessive queueing latency, the CoDel algorithm requires an
  - accurate measure of how long the packets stays in the queue, aka sojourn
  + accurate measure of how long packets stay in the queue, aka their sojourn
  - time. The sojourn time measured at mac80211 layer doesn't include queueing
  + time. The sojourn time measured at the mac80211 layer doesn't include queueing
  - latency in lower layer (firmware/hardware) and CoDel expects lower layer to
  + latency in the lower layer (firmware/hardware) and CoDel expects the lower layer to
	have a short queue. However, most 802.11ac chipsets offload tasks such TX
	aggregation to firmware or hardware, thus have a deep lower layer queue.
  + 
	Without a mechanism to control the lower layer queue size, packets only
  - stays in mac80211 layer transiently before being sent to firmware queue.
  + stay in mac80211 layer transiently before being sent to firmware queue.
	As a result, the sojourn time measured by CoDel in the mac80211 layer is
	almost always lower than the CoDel latency target, hence CoDel does little
	to control the latency, even when the lower layer queue causes excessive
	latency.

  - Byte Queue limits (BQL) is commonly used to address the similar issue with
  + Byte Queue Limits (BQL) are commonly used to address the similar issue with
	wired network interface. However, this method cannot be applied directly
  - to the wireless network interface. Byte is not a suitable measure of queue
  + to the wireless network interface. "Bytes" is not a suitable measure of queue
	depth in the wireless network, as the data rate can vary dramatically from
	station to station in the same network, from a few Mbps to over Gbps.

  - This patch implemented an Airtime-based Queue Limit (AQL) to make CoDel
  + This patch implements an Airtime-based Queue Limit (AQL) to make CoDel
  - works effectively with wireless drivers that utilized firmware/hardware
  + work effectively with wireless drivers that utilize firmware/hardware
  - offloading. AQL only allows each txq to release just enough packets to the
  + offloading. AQL allows each txq to release only enough packets to the
	lower layer to form 1-2 large aggregations to keep hardware fully utilized
  - and keep the rest of frames in mac80211 layer to be controlled by the CoDel
  + and retains the rest of frames in the mac80211 layer to be controlled by the CoDel
	algorithm.