Re:What Can I Do About Bufferbloat?
by wtallis on Tuesday July 03, 2018 @06:25PM
(#17454079)
> For directly managing bufferbloat, I never understood this to be a requirement. Either technique is meant to create back-pressure on the TCP stack so it can more effectively manage it's window.. and both do that perfectly well.
If you have a traffic shaper being fed by a deep, dumb queue, you aren't giving useful back-pressure to TCP until it's too late. You need an AQM that gives either ECN marks or packet drops soon enough that you don't build up or sustain deep queues of packets. That's the core of what bufferbloat is. The queue(s) in front of HTB in your router might not be as stupidly oversized as the queue in your cable or DSL modem, but they're still susceptible to the same problems when there's no AQM component. Some TCPs do a decent job of backing off when latency climbs, before the buffers actually fill and start causing packet drops. But AQM in the router can more directly observe and act on congestion, and works with older TCPs and non-TCP traffic.
If you have a traffic shaper being fed by a deep, dumb queue, you aren't giving useful back-pressure to TCP until it's too late. You need an AQM that gives either ECN marks or packet drops soon enough that you don't build up or sustain deep queues of packets. That's the core of what bufferbloat is. The queue(s) in front of HTB in your router might not be as stupidly oversized as the queue in your cable or DSL modem, but they're still susceptible to the same problems when there's no AQM component. Some TCPs do a decent job of backing off when latency climbs, before the buffers actually fill and start causing packet drops. But AQM in the router can more directly observe and act on congestion, and works with older TCPs and non-TCP traffic.