Slow problem with webservice

I am creating a Python web service on a Linux machine (ubuntu):

import soaplib
import os

from soaplib.core.service import rpc, DefinitionBase, soap
from soaplib.core.model.primitive import String, Integer
from soaplib.core.server import wsgi
from soaplib.core.model.clazz import Array

def runcmd(cmd):
    fout = os.popen(cmd)
    out = fout.read()
    return out

class LinuxServices(DefinitionBase):
@soap(String, String,_returns=Array(String))
def df(self,server, user):
    L = []
    cmd = 'df -hP | grep "/"'
    output = runcmd(cmd).split('\n')
    for n in xrange(len(output)-1):
        out = output[n].split()
        L.append('%s;%s' % (out[5], out[4]))
    return L

if __name__=='__main__':
try:
    from wsgiref.simple_server import make_server
    soap_application = soaplib.core.Application([LinuxServices], 'tns')
    wsgi_application = wsgi.Application(soap_application)
    server = make_server('0.0.0.0', 7789, wsgi_application)
    server.serve_forever()
except ImportError:
    print "Error: example server code requires Python >= 2.5"

I created it based on this example: soaplib helloworld

Then (on Windows 7) I created a Silverlight project, where I use this ws to get the status of a drive on my Linux server:

Service in the Silverlight project:

public class LinuxService
{
    [OperationContract]
    public List<dfItem> df()
    {
        List<dfItem> dfItems = new List<dfItem>();

        WebReference.Application app = new WebReference.Application();

        var result = app.df(new WebReference.df()/*...*/);

        foreach (var item in result.dfResult)
        {
            string[] info = item.Split(';');

            dfItem dfItem = new dfItem()
            {
                MountPoint = info[0].ToString(),
                Usage = info[1].ToString()
            };
            dfItems.Add(dfItem);
        }
        return dfItems;
    }
    //...
}

Service call on page:

protected override void OnNavigatedTo(NavigationEventArgs e)
{
    LinuxServiceClient client = new LinuxServiceClient();

    client.dfCompleted += new EventHandler<dfCompletedEventArgs>(client_dfCompleted);

    client.dfAsync();
}

void client_dfCompleted(object sender, dfCompletedEventArgs e)
{
    DG.ItemsSource = e.Result;
    DG.Visibility = System.Windows.Visibility.Visible;
}

My problem is that when I go to this page, it takes 4-8 seconds to get data from ws (ws on the local network).

I really doubt that line bandwidth can create this latency ...

My question is: Do you have any suggestions on what I can do to speed this up?

System Information:

• UbuntuServer 11.04

• Python: Python 2.7

• Soaplib: soaplib 2.0.0-beta2

• Windows: Windows 7 sp1

• Silverlight: Silverlight 4