kern.hz and single tcp connection throughput

From: Urmas Lett (urmas.lett_at_eenet.ee)
Date: 02/28/05

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Date: Mon, 28 Feb 2005 13:21:37 +0200
To: freebsd-net@freebsd.org

Hello,

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

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

root@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@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@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@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@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@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@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@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@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@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

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