kern.hz and single tcp connection throughput

[Urmas Lett]

Hello,

I was playing with iperf over ~500km empty gigabit link.

FreeBSD 5.3-STABLE
kern.hz="100" (default)

root at test2:~# iperf -c x.x.x.x
------------------------------------------------------------
Client connecting to x.x.x.x, TCP port 5001
TCP window size: 32.5 KByte (default)
------------------------------------------------------------
[  3] local y.y.y.y port 56931 connected with x.x.x.x port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  28.8 MBytes  24.1 Mbits/sec

root at test2:~# iperf -c x.x.x.x -w 64k
------------------------------------------------------------
Client connecting to x.x.x.x, TCP port 5001
TCP window size: 65.0 KByte (WARNING: requested 64.0 KByte)
------------------------------------------------------------
[  3] local y.y.y.y port 57926 connected with x.x.x.x port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  28.3 MBytes  23.6 Mbits/sec

root at test2:~# iperf -c x.x.x.x -w 128k
------------------------------------------------------------
Client connecting to x.x.x.x, TCP port 5001
TCP window size:  129 KByte (WARNING: requested  128 KByte)
------------------------------------------------------------
[  3] local y.y.y.y port 64330 connected with x.x.x.x port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  29.0 MBytes  24.2 Mbits/sec

root at test2:~# iperf -c x.x.x.x -w 256k
------------------------------------------------------------
Client connecting to x.x.x.x, TCP port 5001
TCP window size:  257 KByte (WARNING: requested  256 KByte)
------------------------------------------------------------
[  3] local y.y.y.y port 55575 connected with x.x.x.x port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.1 sec  31.2 MBytes  26.0 Mbits/sec

root at test2:~# iperf -c x.x.x.x -w 512k
------------------------------------------------------------
Client connecting to x.x.x.x, TCP port 5001
TCP window size:  513 KByte (WARNING: requested  512 KByte)
------------------------------------------------------------
[  3] local y.y.y.y port 59043 connected with x.x.x.x port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.2 sec  30.0 MBytes  24.7 Mbits/sec


============================================================
kern.hz="1000"

root at test2:~# iperf -c x.x.x.x
------------------------------------------------------------
Client connecting to x.x.x.x, TCP port 5001
TCP window size: 32.5 KByte (default)
------------------------------------------------------------
[  3] local y.y.y.y port 61402 connected with x.x.x.x port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  44.5 MBytes  37.3 Mbits/sec

root at test2:~# iperf -c x.x.x.x -w 64k
------------------------------------------------------------
Client connecting to x.x.x.x, TCP port 5001
TCP window size: 65.0 KByte (WARNING: requested 64.0 KByte)
------------------------------------------------------------
[  3] local y.y.y.y port 62718 connected with x.x.x.x port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  87.9 MBytes  73.7 Mbits/sec

root at test2:~# iperf -c x.x.x.x -w 128k
------------------------------------------------------------
Client connecting to x.x.x.x, TCP port 5001
TCP window size:  129 KByte (WARNING: requested  128 KByte)
------------------------------------------------------------
[  3] local y.y.y.y port 50571 connected with x.x.x.x port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec   169 MBytes   142 Mbits/sec

root at test2:~# iperf -c x.x.x.x -w 256k
------------------------------------------------------------
Client connecting to x.x.x.x, TCP port 5001
TCP window size:  257 KByte (WARNING: requested  256 KByte)
------------------------------------------------------------
[  3] local y.y.y.y port 61072 connected with x.x.x.x port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec   305 MBytes   255 Mbits/sec

root at test2:~# iperf -c x.x.x.x -w 512k
------------------------------------------------------------
Client connecting to x.x.x.x, TCP port 5001
TCP window size:  513 KByte (WARNING: requested  512 KByte)
------------------------------------------------------------
[  3] local y.y.y.y port 62887 connected with x.x.x.x port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.5 sec   451 MBytes   362 Mbits/sec