RTT and TCP Window size doubts, bandwidth issues

[Marek Salwerowicz]

Hi list,

I am trying to find correct setup of sysctl's for following machines 
(VMs under Vmware Workstation 8) to test large TCP window size:


There are 2 boxes, each of them has following setup:
- % uname -a
FreeBSD freeA 10.1-RELEASE-p6 FreeBSD 10.1-RELEASE-p6 #0: Tue Feb 24 
19:00:21 UTC 2015 
root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC amd64

- 4GB of RAM
- 1 NIC

without any modifications, iperf reports bandwidth speed ~1Gbit/s 
between hosts:

server-side:
# iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 64.0 KByte (default)
------------------------------------------------------------

client-side:

# iperf -c 192.168.108.140
------------------------------------------------------------
Client connecting to 192.168.108.140, TCP port 5001
TCP window size: 32.5 KByte (default)
------------------------------------------------------------
[  3] local 192.168.108.141 port 35282 connected with 192.168.108.140 
port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  1.46 GBytes  1.25 Gbits/sec



I want to simulate (using dummynet) link between hosts with bandwidth 
400mbit/s and latency ~20ms.
In order to do that, I create the ipfw pipe on one box:
IPFW="ipfw -q"


$IPFW pipe 1 config bw 400Mbit/s delay 10ms

$IPFW add 1500 pipe 1 ip from any to any


after running ipfw, bandwidth with default kernel sysctl becomes lower:

client-side:
------------------------------------------------------------
Client connecting to 192.168.108.140, TCP port 5001
TCP window size: 32.5 KByte (default)
------------------------------------------------------------
[  3] local 192.168.108.141 port 35340 connected with 192.168.108.140 
port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.1 sec  12.5 MBytes  10.4 Mbits/sec



I'd like to achieve bandwidth ~400Mbit/s.

I've modified following sysctl's (both on client- and server-side):

kern.ipc.maxsockbuf=33554432  # (default 2097152)

net.inet.tcp.sendbuf_max=33554432  # (default 2097152)
net.inet.tcp.recvbuf_max=33554432  # (default 2097152)

net.inet.tcp.cc.algorithm=htcp  # (default newreno) #enabled in 
/boot/loader.conf also
net.inet.tcp.cc.htcp.adaptive_backoff=1 # (default 0 ; disabled)

net.inet.tcp.cc.htcp.rtt_scaling=1 # (default 0 ; disabled)

net.inet.tcp.mssdflt=1460  # (default 536)

net.inet.tcp.minmss=1300   # (default 216)

net.inet.tcp.rfc1323=1  # (default 1)
net.inet.tcp.rfc3390=1  # (default 1)


net.inet.tcp.sendspace=8388608  # (default 32768)
net.inet.tcp.recvspace=8388608  # (default 65536)

net.inet.tcp.sendbuf_inc=32768  # (default 8192 )
net.inet.tcp.recvbuf_inc=65536  # (default 16384)



But the  results are not really good as I expected:

server-side:
# iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 8.00 MByte (default)
------------------------------------------------------------

client-side:
# iperf -c 192.168.108.140
------------------------------------------------------------
Client connecting to 192.168.108.140, TCP port 5001
TCP window size: 8.00 MByte (default)
------------------------------------------------------------
[  3] local 192.168.108.141 port 21894 connected with 192.168.108.140 
port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.1 sec  24.2 MBytes  20.2 Mbits/sec


I was trying to follow the articles:
- http://www.psc.edu/index.php/networking/641-tcp-tune
- https://fasterdata.es.net/host-tuning/freebsd/

But can't really figure out what / how should be tuned in order to 
achieve good results.

If anyone could find some time and give me some hints, I'd be pleased!


Cheers


Marek