The short version is that when you have multiple processes waiting on listening sockets and a connection arrives, they all get woken up and scheduled to run, but only one will pick up the connection, and the rest have to go back to sleep. These futile wakeups can be a huge waste of CPU, so on systems without accept() scalability fixes, or with more tricky server configurations, the web server puts a lock around accept() to ensure only one process is woken up at a time.
The term (and the fix) dates back to the performance improvement work on Apache 1.3 in the mid-1990s.
The short version is that when you have multiple processes waiting on listening sockets and a connection arrives, they all get woken up and scheduled to run, but only one will pick up the connection, and the rest have to go back to sleep. These futile wakeups can be a huge waste of CPU, so on systems without accept() scalability fixes, or with more tricky server configurations, the web server puts a lock around accept() to ensure only one process is woken up at a time.
The term (and the fix) dates back to the performance improvement work on Apache 1.3 in the mid-1990s.