CC += adrian On 24.11.20 15:45, Toke Høiland-Jørgensen wrote: > Zefir Kurtisi <zefku@xxxxxxxxxxxx> writes: > >> Hi, >> >> I am running into a strange issue with the ath9k operating a 9590 >> device which to me seems like a HW issue, but since work on rate >> controllers is already going for decades, I hardly can imagine this >> never showed up. >> >> The issue observed is this: the TX status descriptors never report >> rateindex 1, it is always 0, 2, or 3, but never 1. >> >> I noticed this by overwriting the rate configuration provided by >> minstrel to a static setup, e.g. (7,3)(5,3)(3,3)(1,3), all MCS. The >> device operates as iperf client to a connected AP and continuously >> transmits data. While at that, the attenuation between the endpoints >> is gradually increased, expecting to see a gradual shift in the >> reported TX status rateindex from 0 to 3. But nada, the values >> reported are 0,2, and 3 - never 1. >> >> I double checked that the TX descriptors are correctly set with the >> rates and retry counts - all looking sane. >> >> More obvious, after changing the rate configuration to >> (7,3)(1,3)(5,3)(3,3) the expectation would be to have either 0 or 1 >> reported as rateidx, since the transmission ought to be successful >> with the lowest rate or never. Again all rates are reported but 1. >> >> Now the question for me is: what is the HW exactly doing with such a >> configuration? Is it skipping the second rate, or is it just reporting >> wrong? > > You should be able to see this by looking at the rates the frames are > being sent at, shouldn't you? > Yes, did that and from there it points to that the second rate is just skipped. Here are some use cases and their sniffing results. Setup is a 11ng STA connected to AP with the attenuation adjusted such that MCS 7 fails, while MCS 5 and below succeed. Monitor is sniffing while sending a single ping from AP to STA. With a rate configuration of (7/2)(3/2)(1/2) we get: 14:02:42.923880 9481489761us tsft 2412 MHz 11n -68dBm signal 65.0 Mb/s MCS 7 20 MHz long GI RX-STBC0 -68dBm signal antenna 0 Data IV: e Pad 20 KeyID 0 14:02:42.923909 9481490037us tsft 2412 MHz 11n -69dBm signal 65.0 Mb/s MCS 7 20 MHz long GI RX-STBC0 -69dBm signal antenna 0 Data IV: e Pad 20 KeyID 0 14:02:42.925244 9481491044us tsft 2412 MHz 11n -68dBm signal 13.0 Mb/s MCS 1 20 MHz long GI RX-STBC0 -68dBm signal antenna 0 Data IV: e Pad 20 KeyID 0 with (7/2)(1/2)(3/2): 13:59:37.073147 9295637087us tsft 2412 MHz 11n -69dBm signal 65.0 Mb/s MCS 7 20 MHz long GI RX-STBC0 -69dBm signal antenna 0 Data IV: c Pad 20 KeyID 0 13:59:37.073467 9295637438us tsft 2412 MHz 11n -69dBm signal 65.0 Mb/s MCS 7 20 MHz long GI RX-STBC0 -69dBm signal antenna 0 Data IV: c Pad 20 KeyID 0 13:59:37.074591 9295638498us tsft 2412 MHz 11n -68dBm signal 26.0 Mb/s MCS 3 20 MHz long GI RX-STBC0 -68dBm signal antenna 0 Data IV: c Pad 20 KeyID 0 and with (7/2)(3/2): 14:04:27.269806 9585836783us tsft 2412 MHz 11n -69dBm signal 65.0 Mb/s MCS 7 20 MHz long GI RX-STBC0 -69dBm signal antenna 0 Data IV: 10 Pad 20 KeyID 0 14:04:27.270342 9585837344us tsft 2412 MHz 11n -68dBm signal 65.0 Mb/s MCS 7 20 MHz long GI RX-STBC0 -68dBm signal antenna 0 Data IV: 10 Pad 20 KeyID 0 14:04:27.271368 9585838370us tsft 2412 MHz 11n -68dBm signal 65.0 Mb/s MCS 7 20 MHz long GI RX-STBC0 -68dBm signal antenna 0 Data IV: 10 Pad 20 KeyID 0 [..] a total of 14 attempts at MCS 7 with the ping finally failing. >> Both possibilities have great impact, since upper layers (like >> airtime) use the returned rateidx to calculate and configure operating >> parameters at runtime. > > Have you actually observed any issues from this? If it's just skipping a > rate, minstrel should still be able to make decisions based on the > actual values returned, no? > The issues arise from the fact that the driver reports a (tx-rateindex/tx-attemp-index) per TX descriptor, leaving the driver to calculate what was put on air based on these two values. If one had rates set to (7/2)(3/7)(1/2) and the TX status reports (tx-rateindex=2/tx-attempt-index=0), driver assumes there were 10 attempts in total while in fact they were 3 when the second rate is skipped. What direct effect this has on RC I can't grasp, but it definitively falsifies statistics. Same goes for airtime: check how this falsifies its calculation in ath_tx_count_airtime(). Also, the above mentioned is an immediate visible issue: if RC provides two rates e.g. (7/3)(5/3) of which the first is too high and the second is not even attempted, frames don't make it through. >> If this is a know issue, nevermind and thanks for pointing me to it. Otherwise if >> some of you have the named device operational, it would help a lot to get the >> issue confirmed. Just apply the attached patch and perform some TX testing in >> either attenuation adjustable or varying link condition setups. Whenever a frame >> is reported to have been transmitted at a rateidx > 0, the collected stats are >> logged, e.g. >> MRR: 2: [51029, 0, 4741, 6454] >> >> In essence, the failure is confirmed if the counter for 1 is 0 or very low >> compared to higher numbers for 0, 2, or 3. > > Tried your patch and couldn't reproduce. Not the same hardware, though. > Mine is: > > 01:00.0 Network controller: Qualcomm Atheros AR9287 Wireless Network Adapter (PCI-Express) (rev 01) > > -Toke > Thanks a lot for trying, let's see if someone else has the affected variant still in use. Cheers, Zefir
