系统内核如下：
centos6.8
[root@localhost ~]# uname -a
Linux localhost.localdomain 2.6.32-642.el6.x86_64 #1 SMP Tue May 10 17:27:01 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

服务器硬盘配置：
2颗CPU，单核12核心，开启超线程
cpu型号：Intel(R) Xeon(R) CPU E5-2690 v3 @ 2.60GHz （41500元一台机器）
共计48线程的逻辑cpu

内存是96G
php程序都是短链接

优化如下：

[root@localhost ~]# cat /etc/sysctl.conf
net.ipv4.ip_forward= 0

kernel.sysrq = 0
kernel.msgmnb = 65536
kernel.msgmax = 65536
kernel.shmmax = 68719476736
kernel.shmall = 4294967296
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_synack_retries = 2
net.ipv4.tcp_syn_retries = 2
vm.overcommit_memory = 1
net.ipv4.tcp_max_syn_backlog = 1638400
net.core.somaxconn = 1638400
net.core.netdev_max_backlog = 20000
net.ipv4.tcp_max_tw_buckets = 1800000
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.tcp_fin_timeout = 10
net.ipv4.tcp_keepalive_time = 90
net.ipv4.ip_local_port_range = 1024 65000
net.ipv4.tcp_window_scaling = 1
net.ipv4.icmp_echo_ignore_all = 0
net.ipv4.icmp_echo_ignore_broadcasts = 1
net.ipv4.tcp_sack = 0
net.ipv4.tcp_keepalive_probes = 5
net.ipv4.tcp_keepalive_intvl = 30
net.ipv4.tcp_retries2 = 5
net.ipv4.tcp_max_orphans = 262144
net.ipv4.tcp_orphan_retries = 3
net.ipv4.tcp_reordering = 5
net.ipv4.tcp_retrans_collapse = 0
net.ipv4.tcp_wmem = 51200 131072 4194304
net.ipv4.tcp_rmem = 51200 131072 4194304
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_tw_recycle = 1

net.netfilter.nf_conntrack_max = 655350
net.netfilter.nf_conntrack_tcp_timeout_established = 90
net.netfilter.nf_conntrack_tcp_timeout_close_wait = 30
net.netfilter.nf_conntrack_tcp_timeout_fin_wait = 60
net.netfilter.nf_conntrack_tcp_timeout_time_wait = 60

[root@localhost ~]#
优化后的并发可以单台服务器可以达到：61525
[root@localhost ~]# date
2017年 11月 29日 星期三 22:23:51 CST
[root@localhost ~]# ss -ant | awk 'NR>1 {++s[$1]} END {for(k in s) print k,s[k]}'
LAST-ACK 327
SYN-RECV 255
ESTAB 61525
FIN-WAIT-1 615
CLOSING 6
FIN-WAIT-2 15732
TIME-WAIT 12157
LISTEN 15
参考地址：
https://www.cnblogs.com/fczjuever/archive/2013/04/17/3026694.html
https://www.cnblogs.com/dasn/articles/5566001.html
linux下修改内核参数进行Tcp性能调优 -- 高并发
https://blog.csdn.net/wwh578867817/article/details/46707389
https://blog.51cto.com/yangrong/1567427