Bandwidth in KVM VM with OpenBSD

Bandwidth in KVM VM with OpenBSD

[Daniel Bareiro]

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Hi all!

I'm using an OpenBSD VM with qemu-kvm 0.12.5 (Debian repositories) and
Linux 2.6.34.5 compiled with the kernel.org sources.

I'm seeing a important difference in the bandwidth when I make a
transfer to or from a OpenBSD VM. Here are some results:

bsd:~# iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 16.0 KByte (default)
------------------------------------------------------------
[  4] local 10.1.0.43 port 5001 connected with 10.1.0.65 port 55049
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  25.2 MBytes  21.1 Mbits/sec
[  4] local 10.1.0.43 port 5001 connected with 10.1.0.65 port 55050
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  25.3 MBytes  21.2 Mbits/sec
[  4] local 10.1.0.43 port 5001 connected with 10.1.0.65 port 55051
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  24.5 MBytes  20.5 Mbits/sec
[  4] local 10.1.0.43 port 5001 connected with 10.1.0.65 port 55054
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  24.1 MBytes  20.2 Mbits/sec
[  4] local 10.1.0.43 port 5001 connected with 10.1.0.65 port 55055
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  26.5 MBytes  22.2 Mbits/sec
[  4] local 10.1.0.43 port 5001 connected with 10.1.0.65 port 55057
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  28.9 MBytes  24.2 Mbits/sec


I also did some tests with scp, presenting a "stalled" state at various
times of the transfer:

ss01:/usr/src# scp linux-2.6.34.5.tar.bz2 viper@bsd:/tmp/
viper@bsd's password:
linux-2.6.34.5.tar.bz2                                                                             100%   65MB   1.3MB/s   00:51


Another test:

ss01:/usr/src# cat linux-2.6.34.5.tar.bz2 | nc -l -p 2222 -q 0

bsd:~# nc ss01 2222 | pv | dd of=/dev/null
64.5MB 0:00:48 [1.32MB/s] [                                                                                                  <=>   ]
132161+1 records in
132161+1 records out
67666495 bytes transferred in 48.766 secs (1387557 bytes/sec)


Using the same test on a Debian GNU/Linux VM:

debian-test2:~# iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
[  4] local 10.1.0.45 port 5001 connected with 10.1.0.65 port 42905
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.1 sec    111 MBytes  92.1 Mbits/sec
[  5] local 10.1.0.45 port 5001 connected with 10.1.0.65 port 42906
[  5]  0.0-10.0 sec    110 MBytes  92.0 Mbits/sec
[  4] local 10.1.0.45 port 5001 connected with 10.1.0.65 port 42907
[  4]  0.0-10.1 sec    110 MBytes  91.6 Mbits/sec
[  5] local 10.1.0.45 port 5001 connected with 10.1.0.65 port 42908
[  5]  0.0-10.0 sec    106 MBytes  88.4 Mbits/sec
[  4] local 10.1.0.45 port 5001 connected with 10.1.0.65 port 42909
[  4]  0.0-10.0 sec    109 MBytes  91.0 Mbits/sec
[  5] local 10.1.0.45 port 5001 connected with 10.1.0.65 port 42910
[  5]  0.0-10.0 sec    107 MBytes  89.4 Mbits/sec

----------------------------------------------------------------------

ss01:/usr/src# scp linux-2.6.34.5.tar.bz2 root@debian-test2:/tmp/
root@debian-test2's password:
linux-2.6.34.5.tar.bz2                                                                             100%   65MB  12.9MB/s   00:05

----------------------------------------------------------------------

ss01:/usr/src# cat linux-2.6.34.5.tar.bz2 | nc -l -p 2222 -q 0

debian-test2:~# nc ss01 2222 | pv | dd of=/dev/null
64,5MB 0:00:04 [14,9MB/s] [          <=>                                                                                           ]
132161+1 records in
132161+1 records out
67666495 bytes (68 MB) copied, 4,3326 s, 15,6 MB/s




In Debian virtual machines I use Virtio (disk only). But this
substantial difference may be due to the use of Virtio or another
reason? The network interface I'm using OpenBSD is a e1000. The network
interface used in Debian virtual machine is a Realtek.

Thanks in advance for your reply.

Regards,
Daniel
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