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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: Thu, 15 Dec 2011 15:03:18 -0000


So the e1000.c and the e1000_hw.h have absolutely no difference between 
the original and the ubuntu version...
The only differences witch refers to the *Intel e1000* in the wall 
sources is this one :

diff -ru qemu//hw/pc_piix.c qemu-kvm-0.14.0+noroms//hw/pc_piix.c
--- qemu//hw/pc_piix.c  2011-12-15 15:37:28.539290000 +0100
+++ qemu-kvm-0.14.0+noroms//hw/pc_piix.c        2011-02-22 
14:34:38.000000000 +0100

@@ -123,7 +141,7 @@
          if (!pci_enabled || (nd->model && strcmp(nd->model, 
"ne2k_isa") == 0))
-            pci_nic_init_nofail(nd, "e1000", NULL);
+            pci_nic_init_nofail(nd, "rtl8139", NULL);

      if (drive_get_max_bus(IF_IDE) >= MAX_IDE_BUS) {


Le 15/12/2011 09:07, Stefan Hajnoczi a écrit :
> On Wed, Dec 14, 2011 at 02:42:12PM -0000, Vincent Autefage wrote:
>> Ok so the *Intel e1000* seems the only card which is impacted by the
>> bug.
> Let me recap with a summary of your debugging:
> QEMU 0.14.0, 0.15.0, and 1.0 built from source all have poor network
> performance below a 20 Mbit/s limit set with tc inside the guest.
> Ubuntu's 0.14.0 QEMU package does not have poor network performance.
> This problem only occurs with the emulated e1000 device.  All other
> emulated NICs operate correctly.
> Now you could diff the e1000 emulation code to get the code changes
> between vanilla and Ubuntu:
>   $ diff -u qemu-0.14.0-vanilla/hw/e1000.c qemu-0.14.0-ubuntu/hw/e1000.c
> (It's possible that there are no significant changes and this bug is
> caused by something outside e1000.c but this is place to check first.)
> Or you could even try copying Ubuntu's e1000.c into the vanilla QEMU
> source tree and retesting to see if the behavior changes.
> 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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