Question on ath10k_mgmt_tx_flush

Ben Greear greearb at
Mon Apr 14 08:45:18 PDT 2014

On 04/13/2014 11:31 PM, Michal Kazior wrote:
> On 11 April 2014 15:25, Ben Greear <greearb at> wrote:
>> On 04/10/2014 10:21 PM, Michal Kazior wrote:
>>> On 10 April 2014 15:41, Ben Greear <greearb at> 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 just want to know if I can skip the sleep if we currently have 2 tx-credits.

>From your answer below, that seems to be a yes.  So, 1/2 of the time (on avg)
is worth the hack to me, and if/when I fix the firmware (and/or if QCA fixes
the firmware), then we should have 2 tx-credits more often and only sleep when
there really is work to do.

>> 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.

What is your preferred fix for this?


> Michał

Ben Greear <greearb at>
Candela Technologies Inc

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