Re: High Latency With Tiered Queues

Linux Advanced Routing and Traffic Control

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ISN Support Staff wrote:
Hello,

  I'm trying to setup what I thought would be a fairly basic tiered
shaping system.  I have a 6mbit (768kbps) link coming into my eth1
device, with my LAN IPs on the eth0 device.  I want to limit outgoing
traffic so that certain IPs are limited to 400kbps, with 3 classes under
that 400k so certain machines get prioritized (main servers in 1:21,
other servers in 1:22, workstations in 1:23)

  The problem is that when I turn this on, my packet latency jumps up by
50 to 100 times the normal rate.  I go from 10-20 ms ping times to
500-1600ms!  I've tried putting SFQ qdiscs under the classes, but that
makes no difference.

  I'm sure there is just some tuning parameter I'm not setting
correctly, but can somebody clue me in to what I'm doing wrong?  Or is
HTB just the wrong scheduler to be using here?  I tried CBQ, but I can't
get the tiers to work ( I keep getting RTNETLINK answers: Invalid
argument)  I'm currently using a single tiered CBQ solution, but it
really doesn't fit my needs.

Here's the full script:
-----------------------
qdisc add dev eth1 root handle 1: htb default 10

Using htb default will send arp to a really long (in this case) backlogged queue, which could cause problems.

Generally you need to classify low latency traffic to different class than bulk if you want it to stay low latency.

I am suprised sfq didn't help - maybe you also need to back off the ceils to allow for overheads on the quoted link speed.

Andy.
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