Re: [Bugreport] ath9k dynack not working/low performance on 5 & 10MHz Bandwidth

[Petrosilius <petrosilius@posteo.de>]

On 22.06.21 13:52, Koen Vandeputte wrote:
>
> On 22.06.21 12:12, Petrosilius wrote:
>> On 22.06.21 11:54, Koen Vandeputte wrote:
>>> On 18.06.21 13:13, Petrosilius wrote:
>>>> Hello Lorenzo Bianconi,
>>>>
>>>> we are running a set of R11e-2HPnD devices and having trouble getting
>>>> dynack working properly.
>>>> Setup:
>>>> * linux-5.4.123
>>>> * OpenWRT (current development branch) with wireless
>>>> backports-5.10.34-1
>>>> * distance 2m between ap and sta
>>>> * Low ambient noise wifi environment
>>>> We experienced some non working dynack or low performance in the
>>>> connection due to too high calculated ackto's.
>>>>
>>>> Here is a ath9k debug output example for a non working dynack @ 10Mhz
>>>> BW:
>>>>
>>>> Wed Jun  2 19:08:50 2021 kern.debug kernel: [  400.500427] ath: phy0:
>>>> {48:8f:5a:3c:bb:03} tx sample 44905341 [dur 8720][h 29-t 30]
>>>> Wed Jun  2 19:08:50 2021 kern.debug kernel: [  400.500437] ath: phy0:
>>>> ack_ts 44844835 st_ts 44905341 st_dur 8720 [17-29]
>>>> Wed Jun  2 19:08:50 2021 kern.debug kernel: [  400.500445] ath: phy0:
>>>> ack_ts 44923425 st_ts 44905341 st_dur 8720 [18-29]
>>>> Wed Jun  2 19:08:50 2021 kern.debug kernel: [  400.554642] ath:
>>>> phy0: rx
>>>> sample 44977693 [h 18-t 20]
>>>> Wed Jun  2 19:08:50 2021 kern.debug kernel: [  400.554701] ath: phy0:
>>>> {48:8f:5a:3c:bb:03} tx sample 44964984 [dur 6032][h 30-t 31]
>>>> Wed Jun  2 19:08:50 2021 kern.debug kernel: [  400.554710] ath: phy0:
>>>> ack_ts 44923425 st_ts 44964984 st_dur 6032 [18-30]
>>>> Wed Jun  2 19:08:50 2021 kern.debug kernel: [  400.554718] ath: phy0:
>>>> ack_ts 44977693 st_ts 44964984 st_dur 6032 [19-30]
>>>> Wed Jun  2 19:08:50 2021 kern.debug kernel: [  400.577890] ath:
>>>> phy0: rx
>>>> sample 45000939 [h 19-t 21]
>>>> Wed Jun  2 19:08:50 2021 kern.debug kernel: [  400.577946] ath: phy0:
>>>> {48:8f:5a:3c:bb:03} tx sample 44998471 [dur 912][h 31-t 32]
>>>> Wed Jun  2 19:08:50 2021 kern.debug kernel: [  400.577956] ath: phy0:
>>>> ack_ts 44977693 st_ts 44998471 st_dur 912 [19-31]
>>>> Wed Jun  2 19:08:50 2021 kern.debug kernel: [  400.577964] ath: phy0:
>>>> ack_ts 45000939 st_ts 44998471 st_dur 912 [20-31]
>>>>
>>>> THe above output is generated in dynack.c by
>>>>
>>>>           ath_dbg(ath9k_hw_common(ah), DYNACK,
>>>>               "ack_ts %u st_ts %u st_dur %u [%u-%u]\n",
>>>>               ack_ts, st_ts->tstamp, st_ts->dur,
>>>>               da->ack_rbf.h_rb, da->st_rbf.h_rb);
>>>>
>>>> The ackto is afterwards calculated by
>>>>
>>>>           if (ack_ts > st_ts->tstamp + st_ts->dur) {
>>>>               ackto = ack_ts - st_ts->tstamp - st_ts->dur;
>>>>
>>>> Filling in the values of the first sample:
>>>>
>>>> (ack_ts > st_ts->tstamp + st_ts->dur) ?
>>>> (44844835 > 44905341+8720) ?
>>>> (44844835 > 44914061) ? ... not given
>>>>
>>>> Therefore a new ackto is not calculated and i can also see that in the
>>>> ack_to file:
>>>>
>>>> 600 A
>>>> 600 A
>>>> 600 A
>>>> ...
>>>>
>>>> These look like the default values to me (and do not change), but
>>>> ath_dynack_get_max_to() should return 750 A for our 10MHz BW case -
>>>> this
>>>> looks also suspecious to me.
>>>>
>>>> For 5 MHz bandwidth there is a ackto calculated (~382 A, looks a
>>>> bit too
>>>> high to me) but the performance is way below expectation (<1MBit)
>>>> For 20 MHz bandwidth there is a ackto calculated (51 A) and the
>>>> performance is fitting the expectation.
>>>> If you want to take a look at the logs for each of these cases for ap
>>>> and sta, you can download them here:
>>>> https://cloud.hs-augsburg.de/s/eworxkJoL6JXYzZ
>>>>
>>>> Did anyone else experience such a behaviour on non 20MHz Channels or
>>>> does anyone have an idea on where this behaviour might originate from?
>>>> I am not experienced in the ath9k driver code, but a uneducated guess
>>>> might be that the ring buffer where the dynack algorithm is taking its
>>>> frame-samples from is not behaving as expected for the 5&10MHz case.
>>>>
>>>> regards,
>>>> julian dorner
>>> Are you stressing the link?
>>> I'll try to simulate this later on
>>>
>>> Regards,
>>>
>>> Koen
>>>
>> Hi Koen,
>>
>> we didnt stress the link that much.
>>
>> There was only SSH from the ap to the sta running to get access to
>> the sta.
>>
>> regards,
>>
>> Julian
>
> Hi,
>
> Please retry while sending data over the link (iperf or so) and let me
> know the results. :)
>
> Thanks,
>
> Koen
>
Hi Koen,

we tried this

> For 5 MHz bandwidth there is a ackto calculated (~382 A, looks a bit too
> high to me) but the performance is way below expectation (<1MBit) 
running iperf didnt help on this.

Regards,

Julian