Linux Kernel 5.15 - upload bandwidth throttled when PCIe slot empty and using jumbo frames

Bug #2028252 reported by Brian Gao
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This bug affects 1 person
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reportbug (Ubuntu)
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Bug Description

Environment
Image version: fossa-onix-adlX171
OS: 22.04.6 (Kernel 5.15.0-72-generic)

Description
Issue: Network upload bandwidth becomes severely throttled on Linux Kernel 5.15 or higher when PCIe slot is empty (from 900M to 100M)

•Only occurs if the PCIe slot in the system is unpopulated (reinstalling the graphics card caused the issue to no longer occur)
•Only occurs if jumbo frames are in use on the network
•Only occurs when MTU frame size is 6500 Bytes or higher, with more severe effects the higher the MTU size (Customer using MTU size 9000)
•Only occurs on Linux kernel version 5.15 or higher (5.14 did not exhibit the issue)

Replication steps:
1.Connect system/server/switch in the below configuration
KYOTOPCFF -> switch(enable jumbo frames) -> KYOTOPCFF

2.Enable jumbo frames on both server and client system with the following command:
ifconfig enp0s31f6 mtu 9000 up
##enp0s31f6 is the "name" of the ethernet interface, and may change depending on what ports are used if the server has more than one NIC

3.Confirm jumbo frames successfully enabled with the following command:
ip a | grep mtu

4.Run the following command on the server to "listen" for the data transfer:
iperf3 -s

5.Run the following command on the Precision 3260:
iperf3 -c <ip address of server> -M 9000
##Lab test example: iperf3 -c 192.168.1.102 -M 9000

Revision history for this message
Brian Gao (briangao) wrote :

Update sos report and we found:
1. kernel 5.14.0-1033 also have this issue.
2. It can be reproduced without a switch.

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