rx rate issue

Michal Kazior michal.kazior at tieto.com
Wed Jul 20 04:03:00 PDT 2016

On 20 July 2016 at 12:50, Sebastian Gottschall <s.gottschall at dd-wrt.com> wrote:
> Am 20.07.2016 um 12:23 schrieb Michal Kazior:
>> On 20 July 2016 at 10:51, Sebastian Gottschall <s.gottschall at dd-wrt.com>
>> wrote:
>>> Hello
>>> while hunting a link stability (packet transmission stop) issue i
>>> discovered
>>> a maybe cosmetic, but maybe als serious issue.
>>> AP is a QCA9880 3x3 card configured as WDS AP
>>> Station is a QCA9880 2x2 card configured as WDS STA
>>> the TX rate of the station matches to the rx rate of the AP.
>>> but the RX rate of the station is wrong as it seems which may be a cause
>>> of
>>> the issue.
>>> could this be a firmware bug on QCA9880?
>>> output of fw_stats
>>> WDS AP:
>>>               Peer MAC address 40:a5:ef:85:4d:6f
>>>                       Peer RSSI 12
>>>                    Peer TX rate 175500
>>>                    Peer RX rate 175500
>>>                Peer RX duration 0
>>> WDS STA:
>>>              Peer MAC address 40:a5:ef:51:49:db
>>>                       Peer RSSI 13
>>>                    Peer TX rate 175500
>>>                    Peer RX rate 351000
>>>                Peer RX duration 0
>> Is this reproducible? Can you try setting a fixed tx bitrate (`iw
>> wlanX set bitrates legacy-5 ht-mcs vht-mcs 1:4` to force vht mcs=4,
>> nss=1) to see if it makes any difference? Perhaps rate-control and tx
>> try-list/status are not parsed properly (for statistical purposes) in
>> firmware which ends up with invalid peer-tx-rate on WDS AP.
> lets try. can you correct the syntax? the following is not correct
> iw dev ath1 set bitrates legacy-5 ht-mcs vht-mcs 1:4
> Usage:  iw [options] dev <devname> set bitrates [legacy-<2.4|5> <legacy rate
> in Mbps>*] [ht-mcs-<2.4|5> <MCS index>*] [v
> ht-mcs-<2.4|5> <NSS:MCSx,MCSy... | NSS:MCSx-MCSy>*] [sgi-2.4|lgi-2.4]
> [sgi-5|lgi-5]
> Sets up the specified rate masks.
> Not passing any arguments would clear the existing mask (if any).

Ah, sorry, my bad.

  iw dev ath1 set bitrates legacy-5 ht-mcs-5 vht-mcs-5 1:4

(ht-mcs and vht-mcs were missing "-5" suffix)

As a sidenote: The logic here is that you need to explicitly tell that
you want empty set of legacy rates and empty set of HT rates and only
a single VHT rate to be set (all explicitly for 5ghz band). This makes
sure that FW rate control is ignored and a fixed rate is used for all
data transmissions (and this should also build tx try-lists without
any fancy retries/fallbacks to different rates).


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