I'm trying to plot the TCP congestion window and the slow start threshold using iperf and the tcp_probe module. I do exactly what is told here:

to obtain the data:

modprobe tcp_probe port=5001
chmod 444 /proc/net/tcpprobe
cat /proc/net/tcpprobe >/tmp/tcpprobe.out &
TCPCAP=$!
iperf -i 10 -t 100 -c receiver
kill $TCPCAP

to plot:

gnuplot -persist <<EOF
set data style linespoints
show timestamp
set xlabel "time (seconds)"
set ylabel "Segments (cwnd, ssthresh)"
plot "/tmp/tcpprobe.out" using 1:7 title "snd_cwnd", \
"/tmp/tcpprobe.out" using 1$8>=2147483647 ? 0 : $8) title "snd_ssthresh"
EOF

I did the test with iperf for 10, 20, 40 100 and 200 seconds but the plot only showed the first 20 seconds in all of the tests. I checked the tcpprobet.out log and y saw that 2048 entries are registered, no matter if the test was for 20 or 200 seconds.

What can I do to solve this?

I'm using ubuntu 10.04 64 bits

I make the same tests with ubuntu 10.04 32 bits on a virtual machine, and it works . I'm going to switch to 32 bits and run the test again. Maybe there is a bug or something else is needed to do in the 64 bits distribution.