调节TCP协议相关参数
--待翻译
The default maximum Linux TCP buffer sizes are way too small. TCP memory is calculated automatically based on system memory; you can find the actual values by typing the following commands:$ cat /proc/sys/net/ipv4/tcp_mem
The default and maximum amount for the receive socket memory:$ cat /proc/sys/net/core/rmem_default
$ cat /proc/sys/net/core/rmem_max
The default and maximum amount for the send socket memory:$ cat /proc/sys/net/core/wmem_default
$ cat /proc/sys/net/core/wmem_max
The maximum amount of option memory buffers:$ cat /proc/sys/net/core/optmem_max
Tune values
Set the max OS send buffer size (wmem) and receive buffer size (rmem) to 12 MB for queues on all protocols. In other words set the amount of memory that is allocated for each TCP socket when it is opened or created while transferring files:
The default value of rmem_max and wmem_max is about 128 KB in most Linux distributions, which may be enough for a low-latency general purpose network environment or for apps such as DNS / Web server. However, if the latency is large, the default size might be too small. Please note that the following settings going to increase memory usage on your server.
# echo 'net.core.wmem_max=12582912' >> /etc/sysctl.conf
# echo 'net.core.rmem_max=12582912' >> /etc/sysctl.conf
You also need to set minimum size, initial size, and maximum size in bytes:# echo 'net.ipv4.tcp_rmem= 10240 87380 12582912' >> /etc/sysctl.conf
# echo 'net.ipv4.tcp_wmem= 10240 87380 12582912' >> /etc/sysctl.conf
Turn on window scaling which can be an option to enlarge the transfer window:# echo 'net.ipv4.tcp_window_scaling = 1' >> /etc/sysctl.conf
Enable timestamps as defined in RFC1323:# echo 'net.ipv4.tcp_timestamps = 1' >> /etc/sysctl.conf
Enable select acknowledgments:# echo 'net.ipv4.tcp_sack = 1' >> /etc/sysctl.conf
By default, TCP saves various connection metrics in the route cache when the connection closes, so that connections established in the near future can use these to set initial conditions. Usually, this increases overall performance, but may sometimes cause performance degradation. If set, TCP will not cache metrics on closing connections.# echo 'net.ipv4.tcp_no_metrics_save = 1' >> /etc/sysctl.conf
Set maximum number of packets, queued on the INPUT side, when the interface receives packets faster than kernel can process them.# echo 'net.core.netdev_max_backlog = 5000' >> /etc/sysctl.conf
Now reload the changes:# sysctl -p
Use tcpdump to view changes for eth0:# tcpdump -ni eth0