OpenvSwitch building, installation and testing problem

Question

I am trying to install OpenvSwitch on Ubuntu 18.04. I have two kernels version which are 5.11.0-27-generic and 5.4.0-42-generic. I set ./configure to build 5.4.0-42-generic version. Then I use command 'make modules_install', and I get the following message

"[openvswitch-2.16.2]make modules_install
cd datapath/linux && make modules_install
make[1]: 進入目錄「/home/user/下載/openvswitch-2.16.2/datapath/linux」
make -C /lib/modules/5.4.0-42-generic/build  M=/home/user/下載/openvswitch-2.16.2/datapath/linux modules_install
make[2]: 進入目錄「/usr/src/linux-headers-5.4.0-42-generic」
INSTALL /home/user/下載/openvswitch-2.16.2/datapath/linux/openvswitch.ko
INSTALL /home/user/下載/openvswitch-2.16.2/datapath/linux/vport-geneve.ko
INSTALL /home/user/下載/openvswitch-2.16.2/datapath/linux/vport-gre.ko
INSTALL /home/user/下載/openvswitch-2.16.2/datapath/linux/vport-lisp.ko
INSTALL /home/user/下載/openvswitch-2.16.2/datapath/linux/vport-stt.ko
INSTALL /home/user/下載/openvswitch-2.16.2/datapath/linux/vport-vxlan.ko
DEPMOD  5.4.0-42-generic
Warning: modules_install: missing 'System.map' file. Skipping depmod.
make[2]: 離開目錄「/usr/src/linux-headers-5.4.0-42-generic」

/sbin/depmod sed -n 's/#define UTS_RELEASE "\([^"]*\)"/\1/p' /lib/modules/5.4.0-42-generic/build/include/generated/utsrelease.h"

The result seems to be success. However, I use mininet to set a topology which have three eths connect to a switch. 'mn --topo=single,3 --controller=none --mac' Next I add a flow that is 'ovs-ofctl add-flow s1 action=normal' and 'pingall' The wireshark gets all icmp packets. I add a code in vport.c in advance. The code is 'printk(KERN_ERR "\r\n!!!print1 !!!\r\n)"' However, dmesg doesn't show printk. I found the 'insmod' command will show the following error 'insmod: ERROR: could not insert module openvswitch.ko: Invalid module format' Is there anything wrong in my building and installation process? How can I show printk message in dmesg?