[Intel-wired-lan] bad iperf3 tcp performance of Intel 10G NIC when MTU is 9000
Alexander Duyck
alexander.duyck at gmail.com
Thu Feb 6 18:18:33 UTC 2020
On Tue, Feb 4, 2020 at 7:34 AM Yi Yang (杨燚)-云服务集团 <yangyi01 at inspur.com> wrote:
>
> Hi, all
>
> We find a very weird issue on Intel 10G NIC, iperf3 tcp performance is good
> when MTU is 1500, but it is about one third of the former when MTU is 9000,
> anybody knows why it is so, is any solution to it available?
>
> The below is our kernel and ixgbe deriver information:
>
> Ubuntu 16.04 and kernel is updated to 4.15.0-36-generic x86_64
> Ixgbe driver version: 5.1.0-k
> Firmware version: 0x61c10001
>
> BTW, tso is on.
There could be quite a few things going on, but it is hard to say
without more information.
What is the test you are running and what are the numbers you are
seeing at 1500 MTU versus 9000 MTU? Have you taken a look at the
"netstat -s" info on both ends to see if anything might be going on
there? One possibility is if you have a congested network moving the
9K MTU frames can be slower as any 9K frames dropped will have to be
retransmitted and since the frames are larger you may encounter the
need for retransmit more often and they would be slower.
Also have you checked the network path to make certain that you are
able to send 9K frames between the two systems? If there are any
switches in between not configured for 9K MTU that could cause
performance issues.
One debugging step you might try would be to incrementally increase
the MTU size and run several tests to see if there is a certain packet
size that the performance drops at. If we find the regression starts
at a certain size it could point to a specific issue either in the
network stack, driver, or the network itself.
Thanks.
- Alex
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