Bufferbloat: the summary

Posted Feb 26, 2011 16:14 UTC (Sat) by hmh (subscriber, #3838)
In reply to: Bufferbloat: the summary by jg
Parent article: The debloat-testing kernel tree

You're likely not going to get anywhere above "acceptable" using a simple AQM, even if it is SFB. It is not going to get to "good" or "excelent" marks.

The Diffserv model got it right, in the sense that even on a simple host, there are flows for which you do NOT want to drop packets (DNS, NTP) if you can help it, and that there is naturally an hierarchy of priorities of which services you'd rather suffer more packet drops than others during congestion.

I've also found that "socializing" the available bandwidth among flows of the same class is a damn convenient thing (SFQ). SFB does this well, AFAIK.

So, I'd say that what we should aim for hosts is an auto-tuned flow-aware AQM that at least pays attention to the bare minimum of priority ordering (802.1p/DSCP class selectors) and does a good job of keeping latency under wraps without killing throughput on high bandwidth-delay product flows. Such a beast could be enabled by default on a distro [for desktops] with little fear.

This doesn't mean you need multiple queues. However, you will want multiple queues in many cases because that's how hardware-assisted QoS works, such as what you find on any 802.11n device or non-el-cheap-o gigabit ethernet NIC.

Routers are a different deal altogether.