TCP Quick ACK (Disable Delayed ACKs, 延迟确认)
Introduction
Enable TCP Quick ACK mode, disabling delayed ACKs.
In quickack mode, ACKs are sent immediately,
rather than delayed if needed in accordance to normal TCP operation.
The TCP_QUICKACK flag is not permanent, it only enables a switch to
or from quickack mode. Subsequent operation of the TCP protocol will
once again enter/leave quickack mode depending on internal protocol
processing and factors such as delayed ack timeouts occurring and data
transfer. This option should not be used in code intended to be portable.
Since Linux 2.4.4.