On 16-05-20 06:11 AM, Eric Dumazet wrote: > On Fri, 2016-05-20 at 09:29 +0200, Jesper Dangaard Brouer wrote: > > >> The hole idea behind allowing bulk qdisc dequeue, was to mitigate this, >> by allowing dequeue to do more work, while holding the lock. >> >> You mention HTB. Notice HTB does not take advantage of bulk dequeue. >> Have you tried to enable/allow HTB to bulk dequeue? >> > > Well, __QDISC___STATE_RUNNING means exactly that : one cpu is dequeueing > many packets from the qdisc and tx them to the device. > > It is generic for any kind of qdisc. > > HTB bulk dequeue would have to call ->dequeue() mutiple times. If you do > this while holding qdisc spinlock, you block other cpus from doing > concurrent ->enqueue(), adding latencies (always the same trade off...) > > HTB wont be anytime soon have separate protections for the ->enqueue() > and the ->dequeue(). Have you looked at this monster ? I did, many > times... >
I came to the conclusion that we just need to rewrite a new modern version of HTB at some point. Easier said than done however. > Note that I am working on a patch to transform __QDISC___STATE_RUNNING > to a seqcount do that we can grab stats without holding the qdisc lock. > > > >
