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

[Vincent Autefage]

Hi,

The problem seems to come from the implementation of the Intel e1000 
network cards (which is the default one used by QEMU).
If you use another one, the problem does not appear ;)

Vince

Le 29/01/2012 05:49, Henrique Rodrigues a écrit :
> 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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