Question on ath10k_mgmt_tx_flush

Question on ath10k_mgmt_tx_flush

[Ben Greear]

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?

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com


_______________________________________________
ath10k mailing list
ath10k@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/ath10k

Re: Question on ath10k_mgmt_tx_flush

[Michal Kazior]

On 10 April 2014 15:41, Ben Greear <greearb@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.


Michał

_______________________________________________
ath10k mailing list
ath10k@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/ath10k

Re: Question on ath10k_mgmt_tx_flush

[Ben Greear]

On 04/10/2014 10:21 PM, Michal Kazior wrote:
> On 10 April 2014 15:41, Ben Greear <greearb@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?

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.

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

Thanks,
Ben


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com


_______________________________________________
ath10k mailing list
ath10k@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/ath10k

Re: Question on ath10k_mgmt_tx_flush

[Michal Kazior]

On 11 April 2014 15:25, Ben Greear <greearb@candelatech.com> wrote:
> On 04/10/2014 10:21 PM, Michal Kazior wrote:
>>
>> On 10 April 2014 15:41, Ben Greear <greearb@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

_______________________________________________
ath10k mailing list
ath10k@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/ath10k

Re: Question on ath10k_mgmt_tx_flush

[Ben Greear]

On 04/13/2014 11:31 PM, Michal Kazior wrote:
> On 11 April 2014 15:25, Ben Greear <greearb@candelatech.com> wrote:
>> On 04/10/2014 10:21 PM, Michal Kazior wrote:
>>>
>>> On 10 April 2014 15:41, Ben Greear <greearb@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.

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?

Thanks,
Ben

> 
> 
> Michał
> 


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com


_______________________________________________
ath10k mailing list
ath10k@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/ath10k

Re: Question on ath10k_mgmt_tx_flush

[Michal Kazior]

On 14 April 2014 17:45, Ben Greear <greearb@candelatech.com> wrote:
> On 04/13/2014 11:31 PM, Michal Kazior wrote:
>> On 11 April 2014 15:25, Ben Greear <greearb@candelatech.com> wrote:
>>> On 04/10/2014 10:21 PM, Michal Kazior wrote:
>>>>
>>>> On 10 April 2014 15:41, Ben Greear <greearb@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.

Problem 1:
If you submit a frame that gets stuck for 10 seconds and you don't
flush it (and you have no idea when it is safe to flush other than
timing this with arbitrary numbers like beacon intervals) and you try
to queue another frame that gets stuck you end up with 0 tx credits.

Problem 2:
If you submit a frame and immediately call tx flush you can end up not
sending out the frame at all or ignoring client power save state I'm
afraid.

I was thinking of a more clever hack that would involve sending dummy
frames (i.e. spurious probe responses) to tickle firmware and force it
replenish tx credit after sending the actual requested mgmt frame.
This is ugly, intrusive, wrong and I'm not even sure if this can even
work.


> 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.

The problem is you don't have a way of knowing if mgmt tx is stuck or
not both because there is no tx completion and tx credits aren't
replenished in a sane way. If any of those were ok, we could have a
wait_for_completion() instead of a msleep() and thus cut down wait
times for frames that don't get stuck.


>>> 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?

Fix the firmware, obviously.

999.999.0.636 uses htt for mgmt tx so the problem doesn't exist there.
That's solely a 10.1 branch issue and I doubt this will be ever fixed
in this branch...


Michał

_______________________________________________
ath10k mailing list
ath10k@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/ath10k

Re: Question on ath10k_mgmt_tx_flush

[Ben Greear]

On 04/14/2014 11:41 PM, Michal Kazior wrote:
> On 14 April 2014 17:45, Ben Greear <greearb@candelatech.com> wrote:
>> On 04/13/2014 11:31 PM, Michal Kazior wrote:
>>> On 11 April 2014 15:25, Ben Greear <greearb@candelatech.com> wrote:
>>>> On 04/10/2014 10:21 PM, Michal Kazior wrote:
>>>>>
>>>>> On 10 April 2014 15:41, Ben Greear <greearb@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?


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?

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...


Thanks,
Ben

> 
> Problem 1:
> If you submit a frame that gets stuck for 10 seconds and you don't
> flush it (and you have no idea when it is safe to flush other than
> timing this with arbitrary numbers like beacon intervals) and you try
> to queue another frame that gets stuck you end up with 0 tx credits.
> 
> Problem 2:
> If you submit a frame and immediately call tx flush you can end up not
> sending out the frame at all or ignoring client power save state I'm
> afraid.
> 
> I was thinking of a more clever hack that would involve sending dummy
> frames (i.e. spurious probe responses) to tickle firmware and force it
> replenish tx credit after sending the actual requested mgmt frame.
> This is ugly, intrusive, wrong and I'm not even sure if this can even
> work.
> 
> 
>> 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.
> 
> The problem is you don't have a way of knowing if mgmt tx is stuck or
> not both because there is no tx completion and tx credits aren't
> replenished in a sane way. If any of those were ok, we could have a
> wait_for_completion() instead of a msleep() and thus cut down wait
> times for frames that don't get stuck.
> 
> 
>>>> 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?
> 
> Fix the firmware, obviously.
> 
> 999.999.0.636 uses htt for mgmt tx so the problem doesn't exist there.
> That's solely a 10.1 branch issue and I doubt this will be ever fixed
> in this branch...
> 
> 
> Michał
> 
> _______________________________________________
> ath10k mailing list
> ath10k@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/ath10k
> 


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com


_______________________________________________
ath10k mailing list
ath10k@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/ath10k

Re: Question on ath10k_mgmt_tx_flush

[Michal Kazior]

On 17 April 2014 03:03, Ben Greear <greearb@candelatech.com> wrote:
> On 04/14/2014 11:41 PM, Michal Kazior wrote:
>> On 14 April 2014 17:45, Ben Greear <greearb@candelatech.com> wrote:
>>> On 04/13/2014 11:31 PM, Michal Kazior wrote:
>>>> On 11 April 2014 15:25, Ben Greear <greearb@candelatech.com> wrote:
>>>>> On 04/10/2014 10:21 PM, Michal Kazior wrote:
>>>>>>
>>>>>> On 10 April 2014 15:41, Ben Greear <greearb@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

_______________________________________________
ath10k mailing list
ath10k@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/ath10k

Re: Question on ath10k_mgmt_tx_flush

[Ben Greear]

On 04/16/2014 11:04 PM, Michal Kazior wrote:
> On 17 April 2014 03:03, Ben Greear <greearb@candelatech.com> wrote:
>> On 04/14/2014 11:41 PM, Michal Kazior wrote:
>>> On 14 April 2014 17:45, Ben Greear <greearb@candelatech.com> wrote:
>>>> On 04/13/2014 11:31 PM, Michal Kazior wrote:
>>>>> On 11 April 2014 15:25, Ben Greear <greearb@candelatech.com> wrote:
>>>>>> On 04/10/2014 10:21 PM, Michal Kazior wrote:
>>>>>>>
>>>>>>> On 10 April 2014 15:41, Ben Greear <greearb@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.

Ok, I will try to fix that issue of credits being replenished in
pairs.  I have been following the twisty paths of the firmware, but
so far I cannot see why the problem should exist...

Thanks for the patience and details below..I think I'm getting
and understanding of the problem now...

Thanks,
Ben

>
>
>> 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
>


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com


_______________________________________________
ath10k mailing list
ath10k@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/ath10k