On Mon, 2018-09-10 at 13:17 +0200, Toke Høiland-Jørgensen wrote:

quoted

quoted

- 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. 

And I guess start would increment the schedule number, which is now
dependent on first

Would mean we could get rid of the 'first'
parameter for next_txq(), so might not be such a bad idea;

Right, that's what I meant.

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?

It may still bounce around CPUs if you call this from other places, but
I suspect that wouldn't be the biggest issue. There are a lot of
calculations going on too...

johannes