Question on ath10k_mgmt_tx_flush

[Michal Kazior]

On 17 April 2014 03:03, Ben Greear <greearb at candelatech.com> wrote:
> On 04/14/2014 11:41 PM, Michal Kazior wrote:
>> On 14 April 2014 17:45, Ben Greear <greearb at candelatech.com> wrote:
>>> On 04/13/2014 11:31 PM, Michal Kazior wrote:
>>>> 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 just want to know if I can skip the sleep if we currently have 2 tx-credits.
>>
>> No, not really. At least not in any sane way I can think of.
>
> I managed to hack the firmware and ath10k today so I can get tx
> rate reported (perhaps at least mostly correctly, even).  Since this
> can only work with my firmware, patch was not sent to the list.
>
>
> So, I'm back to working on this tx-flush issue again.
>
> I may not have been clear in my question above, as your answer makes no
> sense to me :)
>
> My question is:  If the driver/firmware supports max of 2 tx-credits, and we currently
> have 2 tx-credits available (ie, there are no pending things in firmware
> because we have all credits available), then can we skip the sleep when
> flushing?

If you do mgmt_tx+flush without any wait you'll end up disregarding
station powersave or drop frame before it is actually transmitted.
With stock firmware there's no way to wait for wmi mgmt tx completion
other than to sleep because tx credits are replenished in pairs. If
you send a mgmt tx and don't flush you risk getting stuck with next
mgmt tx at which point you can't even flush because you're out of
credits.


> Second question:  Assuming this is true, if I just make sure the firmware
> returns all credits as soon as they are freed up, should that be good
> enough to not waste any time sleeping during flush when we do not need
> to flush?

Yes, this is sufficient as a tx completion but is the most hacky way to do it.


> And even with stock firmware, we should be able to skip the sleep at
> least when we get lucky with current tx-credits-available count...

I don't think you can do that.

Even if you have 2 tx credits available and submit mgmt tx - what do
you do from then on? You won't receive tx credit replenishment when
the tx completes unless you submit flush or another mgmt tx. Flush can
drop frames/disregard powersave and next mgmt tx can get stuck. You
could try pushing dummy mgmt tx (spurious probe resp?) assuming it
never gets stuck but that's way beyond an acceptable workaround..

There really isn't any way other than to have a reliable tx completion
indication so that wmi tx worker can flush mgmt frames if they take
too long to complete.

I'd be happy to proven wrong though.


Michał