Problem with writing fast UDP server

[Gabriel Genellina]

En Thu, 20 Nov 2008 14:24:20 -0200, Krzysztof Retel  
<Krzysztof.Retel at googlemail.com> escribió:
> On Nov 20, 4:00 pm, bieff... at gmail.com wrote:
>> On 20 Nov, 16:03, Krzysztof Retel <Krzysztof.Re... at googlemail.com>
>> wrote:
>>
>> > I am struggling writing fast UDP server. It has to handle around 10000
>> > UDP packets per second. I started building that with non blocking
>> > socket and threads. Unfortunately my approach does not work at all.
>> > I wrote a simple case test: client and server. The client sends 2200
>> > packets within 0.137447118759 secs. The tcpdump received 2189 packets,
>> > which is not bad at all.
>> > But the server only handles 700 -- 870 packets, when it is non-
>> > blocking, and only 670 – 700 received with blocking sockets.
>> > The client and the server are working within the same local network
>> > and tcpdump shows pretty correct amount of packets received.
>
> I wonder if there is a kind of setting for socket to allow no delays?

I've used this script to test sending UDP packets. I've not seen any  
delays.

<code>
"""a very simple UDP test

Usage:

   %(name)s client <remotehost> <message to send|length of message>
       to continuously send messages to <remotehost> until Ctrl-C

   %(name)s server
       to listen for messages until Ctrl-C

Uses port %(port)d. Once stopped, shows some statistics.
Creates udpstress-client.csv or udpstress-server.csv with
pairs (size,time)
"""

import os, sys
import socket
import time

PORT = 21758
BUFSIZE = 4096
socket.setdefaulttimeout(10.0)

def server(port):
     sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
     sock.bind(('',port))
     print "Receiving at port %d" % (port)
     history = []
     print "Waiting for first packet to arrive...",
     sock.recvfrom(BUFSIZE)
     print "ok"
     t0 = time.clock()
     while 1:
         try:
             try:
                 data, remoteaddr = sock.recvfrom(BUFSIZE)
             except socket.timeout:
                 print "Timed out"
                 break
             except KeyboardInterrupt: # #1755388 #926423
                 raise
             t1 = time.clock()
             if not data:
                 break
             history.append((len(data), t1-t0))
             t0 = t1
         except KeyboardInterrupt:
             print "Stopped"
             break
     sock.close()
     return history

def client(remotehost, port, data):
     sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
     history = []
     print "Sending %d-bytes packets to %s:%d" % (len(data), remotehost,  
port)
     t0 = time.clock()
     while 1:
         try:
             nbytes = sock.sendto(data, (remotehost,port))
             t1 = time.clock()
             if not nbytes:
                 break
             history.append((nbytes, t1-t0))
             t0 = t1
         except KeyboardInterrupt:
             print "Stopped"
             break
     sock.close()
     return history

def show_stats(history, which):
     npackets = len(history)
     bytes_total = sum([item[0] for item in history])
     bytes_avg = float(bytes_total) / npackets
     bytes_max = max([item[0] for item in history])
     time_total = sum([item[1] for item in history])
     time_max   = max([item[1] for item in history])
     time_min   = min([item[1] for item in history])
     time_avg = float(time_total) / npackets
     speed_max = max([item[0]/item[1] for item in history if item[1]>0])
     speed_min = min([item[0]/item[1] for item in history if item[1]>0])
     speed_avg = float(bytes_total) / time_total
     print "Packet count       %8d" % npackets
     print "Total bytes        %8d bytes" % bytes_total
     print "Total time         %8.1f secs" % time_total
     print "Avg size / packet  %8d bytes" % bytes_avg
     print "Max size / packet  %8d bytes" % bytes_max
     print "Max time / packet  %8.1f us" % (time_max*1e6)
     print "Min time / packet  %8.1f us" % (time_min*1e6)
     print "Avg time / packet  %8.1f us" % (time_avg*1e6)
     print "Max speed          %8.1f Kbytes/sec" % (speed_max/1024)
     print "Min speed          %8.1f Kbytes/sec" % (speed_min/1024)
     print "Avg speed          %8.1f Kbytes/sec" % (speed_avg/1024)
     print
     open("udpstress-%s.csv" % which,"w").writelines(
         ["%d,%f\n" % item for item in history])

if len(sys.argv)>1:
     if "client".startswith(sys.argv[1].lower()):
         remotehost = sys.argv[2]
         data = sys.argv[3]
         if data.isdigit(): # means length of message
             data = "x" * int(data)
         history = client(remotehost, PORT, data)
         show_stats(history, "client")
         sys.exit(0)
     elif "server".startswith(sys.argv[1].lower()):
         history = server(PORT)
         show_stats(history, "server")
         sys.exit(0)

print >>sys.stderr, __doc__ % {
         "name": os.path.basename(sys.argv[0]),
         "port": PORT}
</code>

Start the server before the client.

-- 
Gabriel Genellina