Re: [Make-wifi-fast] [PATCH v4] ath9k: Switch to using mac80211 intermediate software queues.

["Toke Høiland-Jørgensen" <toke@toke.dk>]

Kalle Valo <kvalo@codeaurora.org> writes:

> Toke Høiland-Jørgensen <toke@toke.dk> writes:
>
>> Kalle Valo <kvalo@codeaurora.org> writes:
>>
>>> Toke Høiland-Jørgensen <toke@toke.dk> writes:
>>>
>>>> This switches ath9k over to using the mac80211 intermediate software
>>>> queueing mechanism for data packets. It removes the queueing inside the
>>>> driver, except for the retry queue, and instead pulls from mac80211 when
>>>> a packet is needed. The retry queue is used to store a packet that was
>>>> pulled but can't be sent immediately.
>>>>
>>>> The old code path in ath_tx_start that would queue packets has been
>>>> removed completely, as has the qlen limit tunables (since there's no
>>>> longer a queue in the driver to limit).
>>>>
>>>> Based on Tim's original patch set, but reworked quite thoroughly.
>>>>
>>>> Cc: Tim Shepard <shep@alum.mit.edu>
>>>> Cc: Felix Fietkau <nbd@nbd.name>
>>>> Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
>>>> ---
>>>> Changes since v3 (most due to Felix; thanks!):
>>>>   - Correctly notify mac80211 when there are packets in the retry queue
>>>>     on powersave start/stop.
>>>>   - Get rid of ath_tx_aggr_resume().
>>>>   - Some readability changes and additional WARN_ON/BUG_ON in
>>>>     appropriate places.
>>>
>>> This is great work but due to the regressions I'm not sure if this
>>> will be ready for 4.9. To get more testing time I wonder if we should
>>> wait for 4.10? IMHO applying this in the end of the cycle is too risky
>>> and we should try to maximise the time linux-next by applying this
>>> just after -rc1 is released.
>>>
>>> Thoughts?
>>
>> Well, now that we understand what is causing the throughput regressions,
>> fixing them should be fairly straight forward (yeah, famous last words,
>> but still...). I already have a patch for the fast path and will go poke
>> at the slow path next. It'll probably require another workaround or two,
>> so I guess it won't be the architecturally clean ideal solution; but it
>> would make it possible to have something that works for 4.9 and then
>> iterate for a cleaner design for 4.10.
>
> But if we try to rush this to 4.9 it won't be in linux-next for long. We
> are now in -rc3 and let's say that the patches are ready to apply in two
> weeks. That would leave us only two weeks of -next time before the merge
> window, which I think is not enough for a controversial patch like this
> one. There might be other bugs lurking which haven't been found yet.

What, other hidden bugs? Unpossible! :)

Would it be possible to merge the partial solution (which is ready now,
basically) and fix the slow path in a separate patch later?

(Just spit-balling here; I'm still fairly new to this process. But I am
concerned that we'll hit a catch-22 where we can't get wider testing
before it's "ready" and we can't prove that it's "ready" until we've had
wider testing...)

-Toke