Re: [Make-wifi-fast] [PATCH RFC v3 0/4] Move TXQ scheduling into mac80211

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

Johannes Berg <johannes@sipsolutions.net> writes:

> On Sat, 2018-09-08 at 00:22 +0200, Toke Høiland-Jørgensen wrote:
>> 
>> A few things that were discussed in the last round that I did *not* change:
>
> Thanks for this list btw.
>
>> - I did not add any locking around next_txq(); the driver is still supposed
>>   to maintain a lock that prevents two threads from trying to schedule the
>>   same AC at the same time. This is what drivers already do, so I figured it
>>   was easier to just keep it that way rather than do it in mac80211.
>
> I'll look at this in the code, but from a maintainer perspective I'm
> somewhat worried that this will lead to issues that are really the
> driver's fault, but surface in mac80211. I don't know how easy it
> would be to catch that.

Yeah, I get what you mean. The alternative would be to have a
ieee80211_start_schedule(ac) and ieee80211_end_schedule(ac), which
basically just takes a lock. Would mean we could get rid of the 'first'
parameter for next_txq(), so might not be such a bad idea; and if the
driver has its own locking the extra locking in mac80211 would just be
an always-uncontested spinlock, which shouldn't be much overhead, right?

-Toke