Re: [Make-wifi-fast] [PATCH] ath9k: Switch to using mac80211 intermediate software queues.

[Felix Fietkau <nbd@nbd.name>]

On 2016-07-04 19:46, Toke Høiland-Jørgensen wrote:
> Tim Shepard <shep@alum.mit.edu> writes:
> 
>> Thanks for unconfusing me a couple weeks ago, and cluing me into how
>> the limit on ->pending_frames is not really relevant for the data
>> packets that go through the new intermediate queues.
>>
>> But I'm not sure if this would allow us to remove the limit on
>> pending_frames because even though normal data packets would not
>> normally build up that many packets, there are other packet types
>> which bypass the intermediate queues and are transmitted directly
>> (also in most cases bypassing the ath9k internal queues in the way
>> ath9k worked before we patched it to use the mac80211 intermediate
>> queues).
> 
> Yes, but, well, since they're not queued they are not going to overflow
> anything. The aggregation building logic stops at two queued aggregates,
> so the default limit of 123 packets is never going to be hit when the
> queue is moved into the mac80211 layer. So keeping the knobs around only
> helps people who purposefully want to cripple their ability to do
> aggregation; and it won't be doing what it promises (limiting qlen),
> since that is now moved out of the driver. So IMO, removing the knobs is
> the right thing to do. I have already updated my patch to do so, which
> I'll send as a v2 once the other bits are resolved.
I agree.

>> Earlier Felix said:
>>
>>> Channel context based queue handling can be dealt with by
>>> stopping/starting relevant queues on channel context changes.
>>
>> But I don't see how to handle the case here where packets get passed
>> to the driver with ath_tx_start() and wind up in the scenario above.
> 
> Well, presumably the upper layers won't try to transmit anything through
> the old TX path if the start/stop logic is implemented properly. The
> chanctx code already seems to call the ieee80211_{start,stop}_queue()
> functions when changing context, so not sure what else is needed. Guess
> I'll go see if I can provoke an actual triggering of the bug, unless
> Felix elaborates on what he means before I get around to it (poke,
> Felix? :)).
Then I guess the logic in ath_tx_start was a leftover from a time before
some queue related rework happened to the chanctx code.
In that case you can simply remove the chanctx related software queueing
stuff from ath_tx_start.

- Felix