Question on ath10k_mgmt_tx_flush

[Michal Kazior]

On 11 April 2014 15:25, Ben Greear <greearb at candelatech.com> wrote:
> On 04/10/2014 10:21 PM, Michal Kazior wrote:
>>
>> On 10 April 2014 15:41, Ben Greear <greearb at candelatech.com> wrote:
>>>
>>> Can we optimize this method to return early if the tx-credits
>>> are fully replenished (ie, == 2) instead of just sleeping the
>>> 2 x beacon-interval?  That would indicate all messages
>>> have been flushed, right?
>>
>>
>> Yeah. You're _almost_ right. Every odd mgmt frame will trigger tx
>> credit replenishment, even if you set NEEDS_CREDITS htc tx flag for
>> all packets. It seems that tx credits aren't replenished until you
>> submit an even number of mgmt tx:
>>
>>   [tx credits =2]
>>   vdev create [-1, =1]
>>   [replenish +1, =2]
>>   mgmt tx [-1, =1]
>>   [frame is seen on air, means it left tx queue, but no replenishment]
>>   vdev set param [-1, =0]
>>   [replenish +1, =1]
>>   mgmt tx [-1, =0]
>>   [frame seen on air]
>>   [replenish +2, =2]
>>
>> However once you flush peer tids you get the tx credit immediately.
>> This means you don't ever reach having 2 mgmt tx consuming 2 tx
>> credits (unless things go terribly terribly wrong at which point it's
>> probably already beyond help).
>>
>> A very ugly hack would be to try and send out mgmt tx in pairs - a
>> requested frame and a dummy frame (such that firmware will not buffer
>> it) so that you use tx credit replenishment as tx completion
>> indication.
>
>
> If you ignore how firmware replenishes the tx-credits for now,
> is it safe to assume that if you have 2 tx-credits while in
> the flush routine, then everything is indeed flushed and
> we can skip the sleep?

You want to always skip the sleep between mgmt tx and flush commands?
I'm afraid this won't work because tx flush command can end up with
queued frame being dropped or transmitted regardless of destination
station powersave state if submitted too soon.


> I imagine both I and the QCA firmware guys can make the
> firmware properly replenish tx-credits one at a time instead
> of the only-on-even/odd behaviour you found.

That would be nice.


> But even without that, we might be able to speed up the
> flush 1/2 of the time?

Yes, although I'm not very fond of the idea of applying a hack on top
of another hack.


Michał