Cherie Cheung wrote:
Hi,
I have been simulating a network using dummynet and evaluating it
I haven't played with dummynet and don't know if there are
additional issues inherent in using dummynet itself...
using netperf. Xen3.0-unstable is used and the VMs are
vmlinuz-2.6.11-xenU. The simulated link is 300Mbps with 80ms RTT.
Using netperf, I sent data using TCP from domain-0 of machine 1 to
domain-0 of machine 2. Then I repeat the experiment, but this time
from VM-1 of machine 1 to VM-1 of machine 2.
However, the performance across the two VMs is substantially worse
than that across domain-0. Here's the result:
FROM VM to VM:
TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to dw10.ucsd.edu
(172.19.222.210) port 0 AF_INET
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
87380 65536 65536 80.28 24.83
Your send message size is exactly your socket size. It is also
the size of the default write buffer. The kernel uses half the
buffer (very roughly) for data
Were you testing with 65536 bytes exactly for some reason?
This is stop and go traffic and normally the kernel doesn't
use the entire buffer to store data - it's roughly half...
Could you test with different send sizes?
FROM domain-0 to domain-0:
TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to damp.ucsd.edu
(137.110.222.236) port 0 AF_INET
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
87380 65536 65536 80.11 280.62
Here's the setting of the network buffer:
net.core.wmem_max = 8388608
net.core.rmem_max = 8388608
net.ipv4.tcp_bic = 1
net.ipv4.tcp_rmem = 4096 87380 8388608
net.ipv4.tcp_wmem = 4096 65536 8388608
Does anyone know why the performance across two VMs is so bad? Any fix
to it? Thank you.
If you just want to improve your peformance, increase your
buffer sizes!
For example:
tcp_rmem = 4096 1398080 8388608
tcp_wmem = 4096 1398080 8388608
Were you seeing losses, queue overflows?
More importantly, how much memory do you have in the system and
how were you allocating it?
thanks,
Nivedita
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