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Subject: Re: [Bugreport] ath9k dynack not working/low performance on 5 & 10MHz
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To:     Petrosilius <petrosilius@posteo.de>, linux-wireless@vger.kernel.org
References: <dd49d9f7-db40-4ab7-f24d-6ab4bbd0bb54@posteo.de>
From:   Koen Vandeputte <koen.vandeputte@citymesh.com>
Message-ID: <fd620847-9786-07d2-23be-dba4cedc9089@citymesh.com>
Date:   Tue, 22 Jun 2021 11:54:37 +0200
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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