CentOS 8 默认的内核是 4.18.x ，查看了一下，默认开启BBR拥塞控制算法。如果要体验新功能，我们还是得升级到最新的内核，下面是 CentOS 8 升级新内核的办法。
[root@localhost ~]# cat /etc/redhat-release
CentOS Linux release 8.1.1911 (Core)
[root@localhost ~]# uname -r
4.18.0-147.el8.x86_64
安装 ELRepo 源并启用 ELRepo 源仓库
[root@localhost ~]# rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
[root@localhost ~]# rpm -Uvh https://www.elrepo.org/elrepo-release-8.0-2.el8.elrepo.noarch.rpm
Retrieving https://www.elrepo.org/elrepo-release-8.0-2.el8.elrepo.noarch.rpm
Verifying... ################################# [100%]
Preparing... ################################# [100%]
Updating / installing...
1:elrepo-release-8.0-2.el8.elrepo ################################# [100%]
[root@localhost ~]# yum --disablerepo="*" --enablerepo="elrepo-kernel" list available
ELRepo.org Community Enterprise Linux Kernel Repository - el8 195 kB/s | 919 kB 00:04
Last metadata expiration check: 0:00:01 ago on Wed 18 Mar 2020 02:59:25 PM CST.
Available Packages
bpftool.x86_64 5.5.9-1.el8.elrepo elrepo-kernel
elrepo-release.noarch 8.1-1.el8.elrepo elrepo-kernel
kernel-ml.x86_64 5.5.9-1.el8.elrepo elrepo-kernel
kernel-ml-core.x86_64 5.5.9-1.el8.elrepo elrepo-kernel
kernel-ml-devel.x86_64 5.5.9-1.el8.elrepo elrepo-kernel
kernel-ml-doc.noarch 5.5.9-1.el8.elrepo elrepo-kernel
kernel-ml-headers.x86_64 5.5.9-1.el8.elrepo elrepo-kernel
kernel-ml-modules.x86_64 5.5.9-1.el8.elrepo elrepo-kernel
kernel-ml-modules-extra.x86_64 5.5.9-1.el8.elrepo elrepo-kernel
kernel-ml-tools.x86_64 5.5.9-1.el8.elrepo elrepo-kernel
kernel-ml-tools-libs.x86_64 5.5.9-1.el8.elrepo elrepo-kernel
kernel-ml-tools-libs-devel.x86_64 5.5.9-1.el8.elrepo elrepo-kernel
perf.x86_64 5.5.9-1.el8.elrepo elrepo-kernel
python3-perf.x86_64 5.5.9-1.el8.elrepo elrepo-kernel
[root@localhost ~]#
安装新内核
[root@localhost ~]# yum -y --enablerepo=elrepo-kernel install kernel-ml kernel-ml-devel
查看默认启动内核
[root@localhost ~]# dnf install grubby
[root@localhost ~]# grubby --default-kernel
/boot/vmlinuz-5.5.9-1.el8.elrepo.x86_64 #正常情况下，会显示安装的最新的内核
[root@localhost ~]# grubby --info=ALL #如果默认的启动内核不是最新的内核，可以使用 grubby --info=ALL 查看所有内核
index=0
kernel="/boot/vmlinuz-5.5.9-1.el8.elrepo.x86_64"
args="ro crashkernel=auto resume=/dev/mapper/cl-swap rd.lvm.lv=cl/root rd.lvm.lv=cl/swap rhgb quiet $tuned_params"
root="/dev/mapper/cl-root"
initrd="/boot/initramfs-5.5.9-1.el8.elrepo.x86_64.img $tuned_initrd"
title="Red Hat Enterprise Linux (5.5.9-1.el8.elrepo.x86_64) 8.1 (Ootpa)"
id="03a5ef24954d4f44a3fa64f9edaa53d1-5.5.9-1.el8.elrepo.x86_64"
index=1
kernel="/boot/vmlinuz-4.18.0-147.el8.x86_64"
args="ro crashkernel=auto resume=/dev/mapper/cl-swap rd.lvm.lv=cl/root rd.lvm.lv=cl/swap rhgb quiet $tuned_params"
root="/dev/mapper/cl-root"
initrd="/boot/initramfs-4.18.0-147.el8.x86_64.img $tuned_initrd"
title="CentOS Linux (4.18.0-147.el8.x86_64) 8 (Core)"
id="03a5ef24954d4f44a3fa64f9edaa53d1-4.18.0-147.el8.x86_64"
index=2
kernel="/boot/vmlinuz-0-rescue-03a5ef24954d4f44a3fa64f9edaa53d1"
args="ro crashkernel=auto resume=/dev/mapper/cl-swap rd.lvm.lv=cl/root rd.lvm.lv=cl/swap rhgb quiet"
root="/dev/mapper/cl-root"
initrd="/boot/initramfs-0-rescue-03a5ef24954d4f44a3fa64f9edaa53d1.img"
title="CentOS Linux (0-rescue-03a5ef24954d4f44a3fa64f9edaa53d1) 8 (Core)"
id="03a5ef24954d4f44a3fa64f9edaa53d1-0-rescue"
[root@localhost ~]# grubby --set-default /boot/vmlinuz-5.5.9-1.el8.elrepo.x86_64 #手工指定
[root@localhost ~]# reboot