Re: [RFC 1/3] mac80211: Add TXQ scheduling API

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

Johannes Berg <johannes@sipsolutions.net> writes:

> On Wed, 2017-10-11 at 16:06 +0200, Toke H=C3=B8iland-J=C3=B8rgensen wrote:
>
>> > Hmm, not sure. We really want this to be scheduled pretty much
>> > immediately because the other side will be waiting for the frames,
>> > and
>> > if we don't get an answer out quickly it'll have to assume we're
>> > broken. I don't know what the limit here is for our firmware, but
>> > we
>> > should really get this out as soon as possible in this case.
>>=20
>> OK. But presumably it can't preempt packets already pushed to the
>> hardware, right?=20
>
> True. If there are still packets scheduled then it needs even more
> driver tricks to drop those back to tx_pending first ...

Only for packets to the same station, right?

>> So telling the driver to immediately schedule a packet,
>> and making sure that the txq it gets from next_txq() is the right one
>> should do the trick? But I guess it's a bit of a roundabout way,
>> which may not be worth it to avoid an extra callback...
>
> Yeah, might work, but remember that we need to mangle the packet, and
> for that we need to know how many packets will go out. E.g. with U-
> APSD, if we tell the driver 8 packets are OK, and it only wants 6, then
> that's acceptable, but we have to tag the last of those with EOSP ...
>
> So one way or another I think we need a separate callback here, and
> perhaps just have the driver do the EOSP tagging, or have a separate
> function to pull the frames so mac80211 can do the tagging, dunno.

Yeah, sounds like it'll need a separate callback, or at least a flag.

What part of the standard do I have to read to learn how this is
supposed to work, BTW? Or even better, is there a resource that
describes how PS works that is more accessible than the standard itself?

> Note that this is only for _some_ drivers, others will implement much
> of this in firmware.

Right, of course. Fun times! :)

-Toke