Felix Fietkau <nbd@xxxxxxxx> writes: > Hi, > > I've take a closer look at the AQL implementation, and I found some > corner cases that need to be addressed soon: > > - AQL estimated airtime does not take into account A-MPDU, so it is > significantly overestimating airtime use for aggregated traffic, > especially on high rates. > My proposed solution would be to check for a running aggregation session > and set estimated tx time to something like: > expected_airtime(16 * skb->len) / 16. This seems reasonable. Not sure if it'll do anything for ath10k (does mac80211 know the aggregation state for that?), but maybe this is not such a big issue on that hardware? > - 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. I can see how it can be a problem that many stations in powersave can block transmissions for *other* stations, though. Maybe an alternative to the driver subtracting airtime could be to have mac80211 do something like this when a station is put into powersave mode: local->aql_total_pending_airtime -= sum(sta->airtime[ac].aql_tx_pending) (where sum is the summation over all ACs) and the reverse when the station wakes back up? That should keep the whole device from throttling but still prevent a big queue building up for that sta when it wakes back up. Would that work, do you think? -Toke
