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

From: Vincent Autefage
Subject: Re: [Qemu-devel] [Bug 899140] Re: Problem with Linux Kernel Traffic Control
Date: Wed, 14 Dec 2011 14:42:12 -0000

Ok so the *Intel e1000* seems the only card which is impacted by the


Le 05/12/2011 12:11, Stefan Hajnoczi a écrit :
> On Mon, Dec 5, 2011 at 10:45 AM, Vincent Autefage
> <address@hidden>  wrote:
>> So we have another problem...
>> The thing is that the 0.14.0 (and all 0.14.0 rc) built from GIT has the
>> same problem.
>> However, the package 0.14.0 from Ubuntu does not has this bug...
> Okay, that's actually a good thing because the issue is now isolated
> to two similar builds: 0.14.0 from source and 0.14.0 from Ubuntu.
> Either there is an environmental difference in the build configuration
> or Ubuntu has applied patches on top of vanilla 0.14.0.
> I think the next step is to grab the Ubuntu 0.14.0 source package and
> rebuild it to confirm that it does *not* have the bug.
> Then it's just a matter of figuring out what the difference is by a
> (manual) bisection.
> Are you using qemu-kvm?  I found Ubuntu's 0.14.0-based package here:
> http://packages.ubuntu.com/natty/qemu-kvm
> Stefan

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  Problem with Linux Kernel Traffic Control

Status in QEMU:

Bug description:

  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.


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