On Wed, 2019-12-11 at 15:04 +0100, Toke Høiland-Jørgensen wrote: > Johannes Berg <johannes@xxxxxxxxxxxxxxxx> writes: > > > Btw, there's *another* issue. You said in the commit log: > > > > This patch does *not* include any mechanism to wake a throttled TXQ again, > > on the assumption that this will happen anyway as a side effect of whatever > > freed the skb (most commonly a TX completion). > > > > Thinking about this some more, I'm not convinced that this assumption > > holds. You could have been stopped due to the global limit, and now you > > wake some queue but the TXQ is empty - now you should reschedule some > > *other* TXQ since the global limit had kicked in, not the per-TXQ limit, > > and prevented dequeuing, no? > > Well if you hit the global limit that means you have 24ms worth of data > queued in the hardware; those should be completed in turn, and enable > more to be dequeued, no? Yes, but on which queues? Say you have some queues - some (Q1-Qn) got a LOT of traffic, and another (Q0) just has some interactive traffic. You could then end up in a situation where you have 24ms queued up on Q1-Qn (with n high enough to not have hit the per-queue AQL limit), right? Say also the last frame on Q0 was dequeued by the hardware, but the tx_dequeue() got NULL because of the AQL limit having been eaten up by all the packets on Q1-Qn. Now you'll no longer get a new dequeue attempt on Q0 (it was already empty last time, so no hardware reclaim to trigger new dequeues), and a new dequeue on the *other* queues will not do anything for this queue. johannes
