[Make-wifi-fast] Multicast IHUs [was: perverse powersave bug with sta/ap mode]

[Dave Taht]

On Thu, Apr 28, 2016 at 10:10 AM, Juliusz Chroboczek
<jch at pps.univ-paris-diderot.fr> wrote:

>> 4) And ya know - it might merely be a (sadly common) bug. Everybody's
>> supposed to wake up for the multicast beacons and get a notification
>> there's more data to come.
>
> Yes, it's obviously a bug.  Just like you, I'm not suprised -- ad-hoc mode
> and power save is the kind of thing that's never tested.


No, this is the kind of thing that normal users of wifi use -
AP/station mode being the most common mode of operation.

adhoc - rarely functional or tested
power save - VERY tested for people that want to save major power,
which is everybody running on battery, pulling out every trick (even
dubious ones) to meet consumption goals (rather than network
connectivity goals).

I do not know to what extent or where the problem I am seeing is
actually happening, I can look at the multicast beacons harder to see
what's going on.

Wifi powersave is not "go to sleep entirely", it is "please wake up on
this schedule (250ms) so I can poke you with more unicast data if I
have any, it also requires (in the spec) that buffering the
accumulated packets be done til that beacon, and multicast packets are
supposed to be sent as CAB ("crap after beacon" in ath9k's
documentation, content after beacon, elsewhere).

The "buffering til you wake up" requirement is hell on trying to roll
a airtime fairness scheduler, or codel, in stack portions....

Certainly many devices simply disassociate when they go to sleep nowadays.

-- 
Dave Täht
Let's go make home routers and wifi faster! With better software!
http://blog.cerowrt.org