Felix Fietkau <nbd@xxxxxxxx> writes: > 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. See my other reply; I'm not convinced this behaviour is wrong :) -Toke
