tcp performance

Zongsheng Zhang zhang at ist.osaka-u.ac.jp
Tue Jan 3 02:09:50 PST 2006


I have confirmed that there is no problem with settings of Dummynet.
When Host-A/B uses Linux, the throughput of RTT=20ms (using Iperf) is
same as that of RTT=0ms.

Host-A/B use FreeBSD v6.0 release. Does anyone have
experience/suggestion for achieving high throughput with FreeBSD?

Michael Vince wrote:
> Zongsheng Zhang wrote:
> 
>> Hi, *,
>>
>> For testing throughput of a TCP connection, the following topology is
>> used:
>>     Host-A ---GB Ethernet--- Dummynet ---GB Ethernet--- Host-B
>>
>> Host-A/B use FreeBSD v6.0. Sysctl parameters of Host-A/B are:
>> kern.ipc.nmbclusters=32768
>> net.inet.tcp.inflight.enable=0
>> net.inet.tcp.sendspace=2097152  # 2M
>> net.inet.tcp.recvspace=2097152  # 2M
>>
>> When RTT in Dummynet is set to 0ms, the throughput (A--B) is about
>> 900Mbps. The buffer size is enough to fill a link bandwidth=800Mbps, and
>> RTT=20ms. However, if RTT is set to 20ms, the throughput is only about
>> 500Mbps.
>>
>> Are there other parameters which are necessary to adjust? Does anyone
>> have suggestion for high throughput?
>>
>> Thanks in advance.
>>
>>  
>>
> What are you following on your hosts? Release/stable or current? I only
> use just release or stable.
> 
> For your middle router try net.inet.ip.fastforwarding or net.isr.direct
> but not at the same time, then try on top enabling polling.
> Personally I found enabling polling worked best combined with
> net.inet.ip.fastforwarding.
> 
> Andre Oppermann claimed in a post just recently he gets best performance
> using just net.inet.ip.fastforwarding without polling but that might be
> for just -current, I am not sure.
> 
> You could also try using current, but if I had to guess you already are?
> 
> Regards,
> Mike
> 
> 

-- 
Zongsheng Zhang
zhang at ist.osaka-u.ac.jp


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