On 2020-02-27 11:07, Toke Høiland-Jørgensen wrote: > Felix Fietkau <nbd@xxxxxxxx> writes: > >> On 2020-02-26 22:56, Toke Høiland-Jørgensen wrote: >>> Felix Fietkau <nbd@xxxxxxxx> writes: >>>> - We need an API that allows the driver to change the pending airtime >>>> values, e.g. subtract estimated tx time for a packet. >>>> mt76 an ath9k can queue packets inside the driver that are not currently >>>> in the hardware queues. Typically if the txqs have more data than what >>>> gets put into the hardware queue, both drivers will pull an extra frame >>>> and queue it in its private txq struct. This frame will get used on the >>>> next txq scheduling round for that particular station. >>>> If you have lots of stations doing traffic (or having driver buffered >>>> frames in powersave mode), this could use up a sizable chunk of the AQL >>>> budget. >>> >>> I'm a bit more skeptical about this. If the driver buffers a bunch of >>> packets that are not accounted that will hurt that station due to extra >>> latency when it wakes up. For ath9k, this is the retry_q you're talking >>> about, right? The number of packets queued on that is fairly limited, >>> isn't it? What kind of powersave buffering is the driver doing, and why >>> can't it leave the packets on the TXQ? That would allow them to be >>> scheduled along with any new ones that might have arrived in the >>> meantime, which would be a benefit for latency. >> For mt76 there should be max. 1 frame in the retry queue, it's just a >> frame that was pulled from the txq in a transmission attempt but that it >> couldn't put in the hw queue because it didn't fit in the current >> aggregate batch. > > Wait, if it's only a single frame that is queued in the driver, how is > this causing problems? We deliberately set the limit so there was a bit > of slack above the size of an aggregate for things like this. Could you > please describe in a bit more detail what symptoms you are seeing of > this problem? :) It would be a single frame per sta/txq. I don't know if it will cause problems in practice, it's just a potential corner case that I found during review. I'd imagine this would probably show up in some benchmarks at least. I'm not seeing any symptoms myself, but I also haven't run any intricate tests yet. - Felix
