Anyone notices that using sfq qdisc adds latency compared to pfifo?
With "sfq perturb 10" ping latency is around 100-120ms, while with "pfifo limit 3" drops to ~10-30ms (qdiscs belong to htb class).
I'm missing something or is this expected?
{
$TC_CLASS parent 1:1 classid 1:20 htb prio 0 rate 900kbit ceil 1000kbit burst 7k
$TC_QDISC parent 1:20 handle 200: {pfifo limit 3} | {sfq perturb 10}
}
There shouldn't really be a queue as such (you still choose one) for your interactive traffic - if you really care about latency HTB should have a class with a high (low number) prio and a high rate (> expected traffic), so other traffic has to borrow.
If you do end up queueing your interractive, then pfifo limit 3 means there will only be 2 packets in front of the ping (I suppose bfifo would be nicer as a fall back - it will penalise big packets more, WRT drops). SFQ default qlen is 128, though the way it works means the delay will depend on how many other connections are queued.
Andy.
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