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Philip Nelson

2010-Jan-31 04:14 UTC

[libvirt-users] poor network performance to one of two guests

G'day, I have a host running two kvm guests. One of them gets very poor
network
performance, testing with iperf I get ~10MBit/sec to guest A, >400MBit/sec to
guest B (running iperf between the host/guest). Both guests are using the same
bridge:

Guest A:
    <interface type='bridge'>
      <mac address='54:52:00:75:24:91'/>
      <source bridge='br0'/>
    </interface>

Guest B:
    <interface type='bridge'>
      <mac address='54:52:00:3b:13:2a'/>
      <source bridge='br0'/>
    </interface>

The host and guests are debian lenny, the host I have updated with some packages
from backports.org. The host is running 2.6.30 with qemu-kvm 0.12.2 and libvirt
0.7.5. The host has 8gig ram and a quad core xeon cpu. Each guest is given one
vcpu, guest A has 3gig memory, guest B 1gig.

I have tried starting them in a different order so that one gets vnet0 and one
gets vnet1, it doesn't make a difference, it's always guest A that is
slow.

I'm a bit stuck here, I don't know what else to try. Below is some
information
for the host/guests, not sure what might be helpful:

ifconfig eth1/br0/vnet0/1 output from the host:

eth1      Link encap:Ethernet  HWaddr 00:25:64:3b:65:de  
          inet6 addr: fe80::225:64ff:fe3b:65de/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:7828 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6664 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:4034843 (3.8 MiB)  TX bytes:466838 (455.8 KiB)
          Interrupt:17 

br0       Link encap:Ethernet  HWaddr 00:25:64:3b:65:de  
          inet addr:192.168.108.1  Bcast:192.168.108.255  Mask:255.255.255.0
          inet6 addr: fe80::225:64ff:fe3b:65de/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:110047 errors:0 dropped:0 overruns:0 frame:0
          TX packets:111420 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:5744145 (5.4 MiB)  TX bytes:870431296 (830.1 MiB)

vnet0     Link encap:Ethernet  HWaddr 72:48:bc:10:45:d4  
          inet6 addr: fe80::7048:bcff:fe10:45d4/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:107881 errors:0 dropped:0 overruns:0 frame:0
          TX packets:581468 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500 
          RX bytes:7129781 (6.7 MiB)  TX bytes:873414210 (832.9 MiB)

vnet1     Link encap:Ethernet  HWaddr 36:20:fc:df:52:66  
          inet6 addr: fe80::3420:fcff:fedf:5266/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:7918 errors:0 dropped:0 overruns:0 frame:0
          TX packets:21692 errors:0 dropped:0 overruns:16236 carrier:0
          collisions:0 txqueuelen:500 
          RX bytes:534843 (522.3 KiB)  TX bytes:32575099 (31.0 MiB)


# brctl show:
bridge name	bridge id		STP enabled	interfaces
br0		8000.0025643b65de	no		eth1
							vnet0
							vnet1
# lsmod | grep kvm
kvm_intel              47336  6 
kvm                   159032  1 kvm_intel

ifconfig output from guest A:
eth0      Link encap:Ethernet  HWaddr 54:52:00:75:24:91  
          inet addr:192.168.108.100  Bcast:192.168.108.0  Mask:255.255.255.0
          inet6 addr: fe80::5652:ff:fe75:2491/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:21708 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8155 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:32576795 (31.0 MiB)  TX bytes:553329 (540.3 KiB)
          Interrupt:10 

ifconfig output from guest B:
eth0      Link encap:Ethernet  HWaddr 54:52:00:3b:13:2a  
          inet addr:192.168.108.101  Bcast:192.168.108.0  Mask:255.255.255.0
          inet6 addr: fe80::5652:ff:fe3b:132a/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:582733 errors:0 dropped:18 overruns:0 frame:0
          TX packets:109328 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:865856730 (825.7 MiB)  TX bytes:7230359 (6.8 MiB)
          Interrupt:10 Base address:0xe000 

Here is the guest A definition:

<domain type='kvm'>
  <name>guestA</name>
  <uuid>a32a9d3b-e5ae-5943-c6db-52bc118f99c6</uuid>
  <memory>3145728</memory>
  <currentMemory>3145728</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type arch='x86_64' machine='pc'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='file' device='disk'>
      <source file='/var/lib/libvirt/images/guestA'/>
      <target dev='vda' bus='virtio'/>
    </disk>
    <disk type='file' device='disk'>
      <source file='/var/lib/libvirt/images/guestA-data.img'/>
      <target dev='vdb' bus='virtio'/>
    </disk>
    <interface type='bridge'>
      <mac address='54:52:00:75:24:91'/>
      <source bridge='br0'/>
    </interface>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes'
keymap='en-us'/>
  </devices>
</domain>

And guest B:

<domain type='kvm'>
  <name>guestB</name>
  <uuid>1816a68e-929c-0b36-41ac-a380a4062298</uuid>
  <memory>1048576</memory>
  <currentMemory>1048576</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type arch='x86_64' machine='pc'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='file' device='disk'>
      <source file='/var/lib/libvirt/images/guestB'/>
      <target dev='vda' bus='virtio'/>
    </disk>
    <disk type='file' device='disk'>
      <source file='/var/lib/libvirt/images/guestB-data.img'/>
      <target dev='vdb' bus='virtio'/>
    </disk>
    <interface type='bridge'>
      <mac address='54:52:00:3b:13:2a'/>
      <source bridge='br0'/>
    </interface>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes'
keymap='en-us'/>
  </devices>
</domain>

Any help would be greatly appreciated.

-- Philip

Philip Nelson

2010-Jan-31 06:53 UTC

head link

[libvirt-users] poor network performance to one of two guests

On Sun, Jan 31, 2010 at 03:14:52PM +1100, Philip Nelson
wrote:> G'day, I have a host running two kvm guests. One of them gets very poor
network
> performance
I think I've figured this out. I created a 3rd guest to test and with iperf
I
was getting nearly 2Gbit/sec. I found the only difference was the interface had
<model type='virtio'/>, so I added that to guest A and then had
much better
network performance. I'm guessing that was ommitted because I had used an
older
version of libvirt/virtinst when initially creating the guest (whichever version
comes with lenny). I still don't know why one guest was much slower than the
other, but it seems like it's all good now.

Cheers

-- Philip

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