tc returns: "quantum of class # is small. Consider r2q change."

Bug #322180 reported by Alwin Garside on 2009-01-28
Affects Status Importance Assigned to Milestone
Alwin Garside

Bug Description

It is documented in HTB manual. The complaint was not displayed before and sharing was silently wrong. Quantum of leaf should be between 1500 and 60000 and it is computed as rate/r2q (or can be supplied independly). So that if your maximal leaf rate is 1Mbit (120000Bps) then r2q should be 3. If max rate is 10kbit (1200Bps) then r2q should be 1. It is warning only and will not affect functionality, only precision. devik

Smallest rate : 16kbit = 2 kilobyt / r2q (=10) = 200. And this is < 1500. So you get warnings. Biggest rate : 100mbit = 12.5 mbyte / r2q = 1.2 Mbyte > 60.000. So you get warnings.

If you do tc qdisc add dev eth0 root handle 1: htb default 10 r2q 1 Smallest rate : 16kbit = 2kilobyte / r2k = 2000. And this is > 1500. So no warnings. Biggest rate : 100mbit = 12.5 mbyte / r2q = 12.5 Mbyte > 60.000. So you get warnings. But you can overrule the quantum : tc class add dev eth0 parent 1:1 classid 1:11 htb rate 128kbit burst 2k quantum 60000

Quantum is used when 2 classes are getting more bandwidth then the rate. So it's only important for sharing the remaining bandwidth. In that case, each class may send quantum bytes.


Alwin Garside (yogarine) on 2009-01-28
Changed in vulpes:
importance: Undecided → Low
status: New → Confirmed
Alwin Garside (yogarine) wrote :

Ok, the trick is that you need to set the r2q on the root qdisc...

So that means the iptable plugin will first have to check what the highest used rate in the qdisc is, and then calculate the lowest possible r2q.

Changed in vulpes:
assignee: nobody → yogarine
status: Confirmed → Triaged
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