[Qemu-devel] [Bug 899140] Re: Problem with Linux Kernel Traffic Control

[Henrique Rodrigues]

Hi guys,

I'm having the same problem with a ubuntu 11.04 (natty) host. I tried to
set the rate controllers using tc both at the host and inside the guest
i.e.:

tc qdisc add vnic0 root tbf rate 20mbit burst 20480 latency 50ms (host - to 
control the traffic going to the guest vm) and
tc qdisc add eth0 root tbf rate 20mbit burst 20480 latency 50ms (guest)

And the results are the same reported initially: ~140kbit/sec. I also
tried to use policing filters at the host but I got the same results.

However, if I use htb I can get reasonable throughputs (~20mbit). I used
these commands (both for host and guest):

tc qdisc add dev <DEV> root handle 1: htb default 255
tc class add dev <DEV> parent 1: classid 1:1 htb rate 20mbit burst 20480
tc filter add dev <DEV> parent 1: prio 255 proto ip u32 match ip src 0.0.0.0/0 
flowid 1:1

It seems that the problem is related with the root qdisc only. Have you
guys found an answer for this?

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https://bugs.launchpad.net/bugs/899140

Title:
  Problem with Linux Kernel Traffic Control

Status in QEMU:
  New

Bug description:
  Hi,

  The last main versions of QEMU (0.14.1, 0.15 and 1.0) have an important 
problem when running on a Linux distribution which running itself a Traffic 
Control (TC) instance.
  Indeed, when TC is configured with a Token Bucket Filter (TBF) with a 
particular rate, the effective rate is very slower than the desired one.

  For instance, lets consider the following configuration :

  # tc qdisc add dev eth0 root tbf rate 20mbit burst 20k latency 50ms

  The effective rate will be about 100kbit/s ! (verified with iperf)
  I've encountered this problem on versions 0.14.1, 0.15 and 1.0 but not with 
the 0.14.0...
  In the 0.14.0, we have a rate of 19.2 mbit/s which is quiet normal.

  I've done the experimentation on several hosts :

  - Debian 32bit core i7, 4GB RAM
  - Debian 64bit core i7, 8GB RAM
  - 3 different high performance servers : Ubuntu 64 bits, 48 AMD Opteron, 
128GB of RAM

  The problem is always the same... The problem is also seen with a
  Class Based Queuing (CBQ) in TC.

  Thanks

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