Re: ieee80211_handle_wake_tx_queue and dynamic ps regression

[Bryan O'Donoghue]

On 10/01/2023 12:44, Bryan O'Donoghue wrote:
> + linux-wireless
> On 10/01/2023 12:35, Bryan O'Donoghue wrote:
> > commit a790cc3a4fad75048295571a350b95b87e022a5a 
> > (wake_tx_queue-broken-23-08-01)
> > Author: Alexander Wetzel <alexander@xxxxxxxxxxxxxx>
> > Date:   Sun Oct 9 18:30:39 2022 +0200
> >
> >      wifi: mac80211: add wake_tx_queue callback to drivers
> >
> > is causing a regression with
> >
> > - CONF_PS = 1
> > - CONF_DYNAMIC_PS = 0
> > - ieee80211_handle_wake_tx_queue
> >
> > In this case we get stuck in a loop similar to this
> >
> > // IEEE80211_CONF_CHANGE_PS
> > [   17.255480] wcn36xx: wcn36xx_change_ps/312 enable
> > [   18.088835] ieee80211_tx_h_dynamic_ps/263 setting 
> > IEEE80211_QUEUE_STOP_REASON_PS
> > [   18.088906] ieee80211_handle_wake_tx_queue/334 entry
> > [   18.091505] ieee80211_dynamic_ps_disable_work/2250 calling 
> > ieee80211_hw_config()
> > [   18.095370] ieee80211_handle_wake_tx_queue/338 wake_tx_push_queue
> >
> > // IEEE80211_CONF_CHANGE_PS
> > [   18.102625] wcn36xx: wcn36xx_change_ps/312 disable
> > [   18.107643] wake_tx_push_queue/303 entry
> >
> > // txq is stopped here reason == IEEE80211_QUEUE_STOP_REASON_PS
> > [   18.107654] wake_tx_push_queue/311 q_stopped bitmask 0x00000002 
> > IEEE80211_QUEUE_STOP_REASON_PS true
> > [   18.107661] wake_tx_push_queue/324 exit
> > [   18.107667] ieee80211_handle_wake_tx_queue/342 exit
> > [   18.115560] ieee80211_handle_wake_tx_queue/334 entry
> > [   18.139937] ieee80211_handle_wake_tx_queue/338 wake_tx_push_queue
> > [   18.145163] wake_tx_push_queue/303 entry
> > [   18.150016] ieee80211_dynamic_ps_disable_work/2252 completed 
> > ieee80211_hw_config()
> >
> > // now we unset IEEE80211_QUEUE_STOP_REASON_PS but too late
> > [   18.151145] wake_tx_push_queue/311 q_stopped bitmask 0x00000002 
> > IEEE80211_QUEUE_STOP_REASON_PS true
> > [   18.155263] ieee80211_dynamic_ps_disable_work/2254 clearing 
> > IEEE80211_QUEUE_STOP_REASON_PS
> > [   18.162531] wake_tx_push_queue/324 exit
> > [   18.162548] ieee80211_handle_wake_tx_queue/342 exit
> > [   18.183639] ieee80211_dynamic_ps_disable_work/2259 cleared 
> > IEEE80211_QUEUE_STOP_REASON_PS
> >
> > // IEEE80211_CONF_CHANGE_PS runs again
> > [   18.215487] wcn36xx: wcn36xx_change_ps/312 enable
> >
> > We get stuck in that loop. Packets getting transmitted is a rare 
> > event, most are dropped.

BTW I considered implementing a wcn36xx specific wake_tx callback - 
which maybe should be done anyway.

I _don't_ see other drivers checking for q_stopped & 
IEEE80211_QUEUE_STOP_REASON_PS

Should they be ?

If they should check IEEE80211_QUEUE_STOP_REASON_PS, then right now, 
they don't. If they shouldn't check IEEE80211_QUEUE_STOP_REASON_PS then 
neither should the generic replacement ieee80211_handle_wake_tx_queue()

---
bod