[Make-wifi-fast] [PATCH RFC v4 3/4] mac80211: Add airtime accounting and scheduling to TXQs

Rajkumar Manoharan rmanohar at codeaurora.org
Wed Sep 26 20:09:07 EDT 2018

On 2018-09-26 02:22, Toke Høiland-Jørgensen wrote:
> Rajkumar Manoharan <rmanohar at codeaurora.org> writes:
>> On 2018-09-16 10:42, Toke Høiland-Jørgensen wrote:
>>> +	if (ret) {
>>> +		clear_bit(IEEE80211_TXQ_AIRTIME_THROTTLE, &txqi->flags);
>>> +		list_del_init(&txqi->schedule_order);
>>> +	} else
>>> +		set_bit(IEEE80211_TXQ_AIRTIME_THROTTLE, &txqi->flags);
>>> +
>> This looks wrong to me. txqi->flags are protected by fq->lock but here
>> it is by active_txq_lock. no?
> Both set_bit() and clear_bit() are atomic operations, so they don't 
> need
> separate locking. See Documentation/atomic_bitops.txt
:( Yeah... I got confused with attached soft lockup in ARM platform.

>>> @@ -3677,6 +3751,7 @@ void ieee80211_txq_schedule_end(struct
>>> ieee80211_hw *hw, u8 ac)
>>>  	struct ieee80211_local *local = hw_to_local(hw);
>>>  	spin_unlock_bh(&local->active_txq_lock[ac]);
>>> +	tasklet_schedule(&local->wake_txqs_tasklet);
>>>  }
>> It is an overload to schedule wake_txqs_tasklet for each txq unlock.
>> Instead I would prefer to call __ieee80211_kick_airtime from
>> schedule_end.
>> Thoughts?
> Yeah, I realise scheduling the whole wake_txqs_tasklet is maybe a bit
> heavy-handed here. However just calling into __ieee80211_kick_airtime()
> means we'll end up recursing back to the same place, which is not good
> either (we could in theory flip-flop between two queues until we run 
> out
> of stack space).
IMHO schedule_start/end is needed for tracking first node to break the 
It is not applicable when the driver calls may_transmit(). It would be 
if active_txq_lock is moved within may_transmit.

> My "backup plan" if the wake_txqs_tasklet turns out to be too heavy was
> to define a new tasklet just for this use; but wanted to see if this
> actually turned out to be a problem first...
Instead of adding new tasklet, we can introduce new API to iterate 
throttled txqs. Driver that make use of may_transmit, have to call this 
new API
at the end of irq handler i.e after processing tx/rx.

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