Some questions about I/O Graphs results

asked 2024-12-11 08:14:05 +0000

certainly
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Hello everybody! I am running an iperf3 test between two Server and the test bandwidth is about 10Gb/s (which is also the link bandwidth).

However, in the I/O graph, when the granularity is 1ms, the rate exceeds 10Gb/s（the highest moment can even reach about 15Gb/s）, but when using the granularity of 10ms, everything looks normal again.What's wrong with this?

In addition, when drawing I/O graphs, in addition to the regular granularity (such as 1ms, 10ms), there are also some intervals such as 100ms{2 ?}100ms{5 ?}What does this mean?

Looking forward to everyone reply and have a nice day~

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Pretty hard to answer those questions without any visual information. I guess it also depends a lot exactly where the capture file was taken.

hugo.vanderkooij ( 2024-12-11 08:28:39 +0000 )edit

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answered 2024-12-11 08:29:21 +0000

SYN-bit

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Regarding the exceeding bandwidth, how did you capture the packets? If it was not on a specialized capture system, than chances are great that the timestamping is off. On a general system, packets get queued for a while and then processed all in one go. As the timestamping is done after the queuing you can see packets having delta timestamps that are not physically possible. Like on 1 Gbit/s each full-size packet should be about 12,5 microseconds apart, but I often see 2 microseconds delta time for a few packets and then a larger delta. So in the short interval that only contains the packets with the 2 microsecond intervals, the shown bandwidth in the IO graph will be higher than the physical bandwidth of the link.

Regarding the 100ms{2 ?} etc, I do not see that in my Wireshark 4.4.2 on MacOS. Perhaps you can share your OS and Wireshark version information and post a screenshot somewhere and link to it here to further analyse.

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Thank you very much for your reply！ I'm really sorry I didn't provide a screenshot, because it seems I don't have enough points... I am now importing images using the URL,but it seems that there are some problems with the image parsing. You can open the link directly.

This is the screenshot when the time slot is set to 1ms：

https://imgur.com/a/Z4RTRO3

Below are the screenshots of 2ms and 5ms. It seems that the results are gradually returning to correct：

https://imgur.com/xKTdUpo

https://imgur.com/flChM1k

This is thescreenshot when the time slot is set to 10ms：

https://imgur.com/a/Zn8i2m4

My system is Ubuntu 24.04 LTS. I have not made any changes to the packet capture. How should I modify it to turn on the timestamp?

On the other hand, my wireshark version is Version 4.0.14 ...(more)

certainly ( 2024-12-11 09:16:29 +0000 )edit

More specifically, I executed the command: tcpdump -i ens2f1np1 -s 0 -w /home/iperf10.cap on ubuntu 24.04, and then transferred it to the window server for wireshark analysis. Looking forward to your reply, thanks!

certainly ( 2024-12-11 09:21:04 +0000 )edit

I have looked at the captured logs in detail, and it seems that each packet has a detailed timestamp? Is there any problem here? Thank you！

https://imgur.com/a/SKKqbfz

certainly ( 2024-12-11 09:29:03 +0000 )edit

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Some questions about I/O Graphs results

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