速率显示单位

A letter specifying the format to print bandwidth numbers in. Supported formats are 

    'k' = Kbits/sec           'K' = KBytes/sec
    'm' = Mbits/sec           'M' = MBytes/sec

设置每次报告之间的时间间隔，单位为秒。

Sets the interval time in seconds between periodic bandwidth, jitter, and loss reports. If non-zero, a report is made every interval seconds of the bandwidth since the last report. If zero, no periodic reports are printed. Default is zero.

指定要传输的文件。

client-side: read from the file and write to the network, instead of using random data;
server-side: read from the network and write to the file, instead of throwing the data away.

设置cpu的亲和性，可以指定某一个逻辑cpu运行。

Set the CPU affinity, if possible (Linux and FreeBSD only). On both the client and server you can set the local affinity by using the n form of this argument (where n is a CPU number). In addition, on the client side you can override the server’s affinity for just that one test, using the n,m form of argument. Note that when using this feature, a process will only be bound to a single CPU (as opposed to a set containing potentialy multiple CPUs).

限制测试带宽。UDP 默认为 1Mbit/秒，TCP 默认无限制

Set target bandwidth to n bits/sec (default 1 Mbit/sec for UDP, unlimited for TCP). If there are multiple streams (-P flag), the bandwidth limit is applied separately to each stream. You can also add a ’/’ and a number to the bandwidth specifier. This is called "burst mode". It will send the given number of packets without pausing, even if that temporarily exceeds the specified bandwidth limit.

以时间为测试结束条件进行测试，默认为 10 秒

The time in seconds to transmit for. iPerf normally works by repeatedly sending an array of len bytes for time seconds. Default is 10 seconds. See also the -l, -k and -n options.

以数据传输大小为测试结束条件进行测试

The number of buffers to transmit. Normally, iPerf sends for 10 seconds. The -n option overrides this and sends an array of len bytes num times, no matter how long that takes. See also the -l, -k and -t options.

以传输数据包数量为测试结束条件进行测试

The number of blocks (packets) to transmit. (instead of -t or -n) See also the -t, -l and -n options.

读写缓冲区的长度，TCP 默认为 128K，UDP 默认为 8K；

The length of buffers to read or write. iPerf works by writing an array of len bytes a number of times. Default is 128 KB for TCP, 8 KB for UDP. See also the -n, -k and -t options.

设置套接字缓冲区大小，TCP 模式下为窗口大小；

Sets the socket buffer sizes to the specified value. For TCP, this sets the TCP window size. (this gets sent to the server and used on that side too)

设置 TCP/SCTP 最大分段长度（MSS，MTU 减 40 字节）

Attempt to set the TCP maximum segment size (MSS). The MSS is usually the MTU - 40 bytes for the TCP/IP header. For ethernet, the MSS is 1460 bytes (1500 byte MTU).

设置 TCP/SCTP no delay，屏蔽 Nagle 算法；

Set the TCP no delay option, disabling Nagle's algorithm. Normally this is only disabled for interactive applications like telnet.

    IPTOS_LOWDELAY     minimize delay        0x10
    IPTOS_THROUGHPUT   maximize throughput   0x08
    IPTOS_RELIABILITY  maximize reliability  0x04
    IPTOS_LOWCOST      minimize cost         0x02

设置 IPv6 流标签

Set the IPv6 flow label (currently only supported on Linux).

使用 “zero copy”（零拷贝）方法发送数据；

Use a "zero copy" method of sending data, such as sendfile(2), instead of the usual write(2). This uses much less CPU.

忽略前 n 秒的测试

Omit the first n seconds of the test, to skip past the TCP TCP slowstart period.

设置 TCP 拥塞控制算法

Set the congestion control algorithm (Linux only for iPerf 3.0, Linux and FreeBSD for iPerf 3.1).