CentOS7升级内核并开启BBR

# CentOS7升级内核并开启BBR
## BBR
BBR是拥塞控制算法，传统拥塞控制算法如：RENO CUBIC当出现拥塞时，会大幅减少发送数据窗口，导致传输速率降低。开启BBR可以优化丢包率较高的线路的带宽使用率。

## 内核升级

升级内核有多种方法，小版本升级可以用 yum update 直接搞定，大版本升级有源码升级和 ELRepo 库升级两种方法。

## 安装 ELRepo 库
[ELRepo官网连接](http://elrepo.org/tiki/HomePage "ELRepo官网连接")
```
rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
yum install https://www.elrepo.org/elrepo-release-7.el7.elrepo.noarch.rpm
```

## 安装新版本内核
1. 查看当前内核版本

```shell
[root@ihoiwan maintaintools]# uname -r
3.10.0-957.21.3.el7.x86_64
```

2. 安装新版内核

```shell
# 查看长期支持版内核信息
[root@ihoiwan maintaintools]# yum --disablerepo=\* --enablerepo=elrepo-kernel info kernel-lt
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * elrepo-kernel: mirror-hk.koddos.net
Available Packages
Name        : kernel-lt
Arch        : x86_64
Version     : 5.4.140
Release     : 1.el7.elrepo
Size        : 50 M
Repo        : elrepo-kernel
Summary     : The Linux kernel. (The core of any Linux-based operating system.)
URL         : https://www.kernel.org/
License     : GPLv2
Description : This package provides the Linux kernel (vmlinuz), the core of any
            : Linux-based operating system. The kernel handles the basic functions
            : of the OS: memory allocation, process allocation, device I/O, etc.

# 开始安装，记得提前备份系统
[root@ihoiwan maintaintools]# yum --disablerepo=\* --enablerepo=elrepo-kernel install kernel-lt
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * elrepo-kernel: mirror-hk.koddos.net
Resolving Dependencies
--> Running transaction check
---> Package kernel-lt.x86_64 0:5.4.140-1.el7.elrepo will be installed
--> Finished Dependency Resolution

Dependencies Resolved

=================================================================================================================================================================== Package                             Arch                             Version                                        Repository                               Size
===================================================================================================================================================================Installing:
 kernel-lt                           x86_64                           5.4.140-1.el7.elrepo                           elrepo-kernel                            50 M

Transaction Summary
===================================================================================================================================================================Install  1 Package

Total download size: 50 M
Installed size: 227 M
Is this ok [y/d/N]: y
Downloading packages:
kernel-lt-5.4.140-1.el7.elrepo.x86_64.rpm                                                                                                   |  50 MB  00:00:04     
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : kernel-lt-5.4.140-1.el7.elrepo.x86_64                                                                                                           1/1 
  Verifying  : kernel-lt-5.4.140-1.el7.elrepo.x86_64                                                                                                           1/1

Installed:
  kernel-lt.x86_64 0:5.4.140-1.el7.elrepo

Complete!
# 安装成功！检查一下
[root@ihoiwan maintaintools]# rpm -qa |grep kernel-lt
kernel-lt-5.4.140-1.el7.elrepo.x86_64
```

3. 修改启动内核版本
```
# 查看当前内核版本
[root@ihoiwan ~]# grub2-editenv list
saved_entry=CentOS Linux (3.10.0-957.21.3.el7.x86_64) 7 (Core)
# 查看启动项
[root@ihoiwan ~]# cat /boot/grub2/grub.cfg |grep "CentOS Linux"
menuentry 'CentOS Linux (5.4.140-1.el7.elrepo.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-957.el7.x86_64-advanced-1114fe9e-2309-4580-b183-d778e6d97397' {
menuentry 'CentOS Linux (3.10.0-957.21.3.el7.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-957.el7.x86_64-advanced-1114fe9e-2309-4580-b183-d778e6d97397' {
menuentry 'CentOS Linux (3.10.0-957.el7.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-957.el7.x86_64-advanced-1114fe9e-2309-4580-b183-d778e6d97397' {
menuentry 'CentOS Linux (0-rescue-20190711105006363114529432776998) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-0-rescue-20190711105006363114529432776998-advanced-1114fe9e-2309-4580-b183-d778e6d97397' {
# 一共有四条启动项，我们要是用的是新安装的版本所以，修改默认启动项
[root@ihoiwan ~]# grub2-set-default 'CentOS Linux (5.4.140-1.el7.elrepo.x86_64) 7 (Core)'
[root@ihoiwan ~]# grub2-editenv list
saved_entry=CentOS Linux (5.4.140-1.el7.elrepo.x86_64) 7 (Core)
```

## 开启BBR
修改完启动项以后，开启BBR
```
# 查看当前使用的阻塞控制算法
[root@ihoiwan ~]# sysctl net.ipv4.tcp_available_congestion_control
net.ipv4.tcp_available_congestion_control = cubic reno
# 修改为BBR
[root@ihoiwan ~]# cat >> /etc/sysctl.conf <<\EOF
# ENABLE Google BBR 
net.ipv4.tcp_congestion_control = bbr
net.core.default_qdisc = fq

EOF
[root@ihoiwan ~]# reboot
# 已经升级到5.4
[root@ihoiwan ~]# uname -r
5.4.140-1.el7.elrepo.x86_64
# BBR 已开启
[root@ihoiwan ~]# sysctl net.ipv4.tcp_available_congestion_control
net.ipv4.tcp_available_congestion_control = reno cubic bbr
```