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I have 2 Lenovo ThinkPads running Ubuntu with a 1 meter ethernet cable between them, both having standard Intel Ethernet adapters.
The ping between the two is about 300 us (microseconds).
This seems quite high; why is it? I have read that 1 GbE can typically achieve 40 us latency.
Is this the minimum latency I can expect, or is there software tuning I can perform to reduce this latency? What is the bottleneck? Is it Linux? On this gamer web site for Windows the tool in the screenshot seems to suggest 40 us latency in most cases.
nh2
Posted 2016-09-05T17:57:01.437
Reputation: 797
Many, possibilities. Need to know specs. If you don't have a fast enough CPU and enough RAM it could slow it down. Which Ubuntu if it has an old kernel that also could impact it. uname -r If you don't have a 4.x kernel upgrade. – cybernard – 2016-09-05T18:04:46.330
@cybernard ThinkPad T440, Ubuntu 16.04's kernel (which is a 4.4). There is no CPU usage apparent from the
ping(it would indeed suprise me ifpingexhausted my CPU or RAM). – nh2 – 2016-09-05T18:50:42.317Not ping exhausting your CPU, but something else using 99% of the CPU and then you run ping at the same time. – cybernard – 2016-09-05T18:53:08.893
@cybernard Ah OK -- both machines are completely idle and have 7 GB of free RAM. – nh2 – 2016-09-05T19:06:08.020
Just to be clear, I don't think there's anything wrong with the machines. I've seen this kind of roughly-half-a-millisecond-ethernet-ping between many devices already. I'm just wondering why it is this high, in general. I'm hoping it is an unfortunate default in Linux. – nh2 – 2016-09-05T19:07:41.703
do you have hardware offloading enabled? – cybernard – 2016-09-05T19:08:28.010
ethtool --show-offload eth0 You just have to test it both ways on and off on both machines. ethtool --offload eth0 rx on tx on also ethtool --offload eth0 gso on tso on – cybernard – 2016-09-05T19:27:40.170
@cybernard Unfortunately none of these offloading changes have made any difference to my
ping. – nh2 – 2017-09-18T00:23:36.130Given no answers, I have reposted this question at ServerFault, where more people familiar with network tuning might be watching. Unfortunately I can't move it there instead of reposting because I don't have enough reputation here.
– nh2 – 2017-09-18T00:35:04.973