Xen users - Nov 2005 - Network performance in virtual machine (good upload speed, bad download)

I have just installed Xen and got a virtual machine up and running.  
Everything seems to work fine, except that I get strange network  
performance in the virtual machine. When I upload data, I get good  
speeds, around 6-7 MB/s which I think is ok on a 100 Mbit network.  
When I download however, I only get ~300 KB/s. On the host machine I  
get good speed in both direction.
The version of Xen is 2.0.7, and I have tried both the binary release  
and built my own kernel, with the same results. The host OS is debian  
sarge. I really have no idea where to look for a solution, so every  
advice I can get is highly appreciated.

Best regards,
/Martin

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hi,

networking problems with large MTU''s have been recently discussed on
the xen-devel list.
i don''t know if this is also relevant for xen 2.0.7, but as a first
step, i would take a look of
the bridge''s MTU as well as of the virtual eth device in the domU.

greetings

stephan



Martin Nilsson schrieb:
> I have just installed Xen and got a virtual machine up and running.
> Everything seems to work fine, except that I get strange network
> performance in the virtual machine. When I upload data, I get good
> speeds, around 6-7 MB/s which I think is ok on a 100 Mbit network.
> When I download however, I only get ~300 KB/s. On the host machine
> I get good speed in both direction. The version of Xen is 2.0.7,
> and I have tried both the binary release and built my own kernel,
> with the same results. The host OS is debian sarge. I really have
> no idea where to look for a solution, so every advice I can get is
> highly appreciated.
>
> Best regards, /Martin
>
> _______________________________________________ Xen-users mailing
> list Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users


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Martin Nilsson wrote:
> performance in the virtual machine. When I upload data, I get good  
> speeds, around 6-7 MB/s which I think is ok on a 100 Mbit network.  When 
> I download however, I only get ~300 KB/s. On the host machine I  get 
> good speed in both direction.
Check that your NIC is set for full duplex, I have seen symptoms like 
you mention (outside of Xen) whenever the NIC is half-duplex.

As a rule we always use the following command on 100Mb interfaces:

   ethtool -s ethX autoneg off duplex full speed 100

Good luck,
Fraser

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This is my output from ifconfig:

lucy:~# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:02:A5:0D:09:32
           inet addr:192.168.1.10  Bcast:192.168.1.255  Mask: 
255.255.255.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:5951 errors:23 dropped:23 overruns:0 frame:23
           TX packets:3630 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:7130145 (6.7 MiB)  TX bytes:378644 (369.7 KiB)

lo        Link encap:Local Loopback
           inet addr:127.0.0.1  Mask:255.0.0.0
           UP LOOPBACK RUNNING  MTU:16436  Metric:1
           RX packets:3606 errors:0 dropped:0 overruns:0 frame:0
           TX packets:3606 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:269811 (263.4 KiB)  TX bytes:269811 (263.4 KiB)

vif1.0    Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:2547 errors:0 dropped:0 overruns:0 frame:0
           TX packets:4773 errors:0 dropped:199 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:175603 (171.4 KiB)  TX bytes:6725419 (6.4 MiB)

xen-br0   Link encap:Ethernet  HWaddr 00:02:A5:0D:09:32
           inet addr:192.168.1.10  Bcast:192.168.1.255  Mask: 
255.255.255.255
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:1196 errors:0 dropped:0 overruns:0 frame:0
           TX packets:1085 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:140820 (137.5 KiB)  TX bytes:203365 (198.5 KiB)

Should I perhaps try a lower MTU? I''ve never worked with bridges in  
Linux before, so I''m not sure.

Best regards,
/Martin


28 nov 2005 kl. 01.45 skrev Stephan Seitz:
> hi,
>
> networking problems with large MTU''s have been recently discussed
on
> the xen-devel list.
> i don''t know if this is also relevant for xen 2.0.7, but as a
first
> step, i would take a look of
> the bridge''s MTU as well as of the virtual eth device in the domU.
>
> greetings
>
> stephan
>
>
>
> Martin Nilsson schrieb:
>
>> I have just installed Xen and got a virtual machine up and running.
>> Everything seems to work fine, except that I get strange network
>> performance in the virtual machine. When I upload data, I get good
>> speeds, around 6-7 MB/s which I think is ok on a 100 Mbit network.
>> When I download however, I only get ~300 KB/s. On the host machine
>> I get good speed in both direction. The version of Xen is 2.0.7,
>> and I have tried both the binary release and built my own kernel,
>> with the same results. The host OS is debian sarge. I really have
>> no idea where to look for a solution, so every advice I can get is
>> highly appreciated.
>>
>> Best regards, /Martin
>>
>> _______________________________________________ Xen-users mailing
>> list Xen-users@lists.xensource.com
>> http://lists.xensource.com/xen-users
>
>
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
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