On Wed, 2012-05-16 at 12:31 +0300, Jonathan Morton wrote: > There are two goals here. One: provide real feedback to TCPs so that > they know when the link is full and thus don't also fill up the buffer > constantly. Two: prevent flows from unduly interfering with each > other, so they don't have to fill the buffer just to be sure of good > throughput. > > What you seem to be saying is that you have a queue full of > unresponsive flows that aren't being dropped because they have ECN > support and are being marked instead. With FQ, that doesn't matter > because other flows can still get through with low latency, and in > fq_codel they are treated separately for mark/drop decision purposes. > And if the queue really does fill up physically, codel already drops > packets at head regardless of ECN capability.
It matters because : 1) We setup high limit for codel so "head drop" at enqueue time is a last resort thing. 2) If you have ECN blackhole _after_ you, flow can be non responsive not because it doesnt want to, only because of the blackhole. Detecting a too long delay in this flow queue and reverting to drops instead of marks can help to recover from ECN blackhole. _______________________________________________ Bloat mailing list [email protected] https://lists.bufferbloat.net/listinfo/bloat
