Threaded Device Probing
This page describes Threaded device probing, which is a feature which allows drivers in the Linux kernel to have their probes execute in parallel threads. One of the most time-consuming parts of the boot up sequence is the probing by device drivers for their hardware devices.
This patch was created by Greg Kroah-Hartman and with it he was able to reduce the bootup time of the kernel on one machine by about 400 milliseconds.
Original post and discussion
See this article for the original description of this and a patch.
There was discussion about this here.
Greg Kroah-Hartman posted a patch to LKML on Sep 25 2006 with a config option to turn this on for the PCI bus. His post is at: lkml thread
The kernel option to turn on this feature for the PCI bus in Linux version 2.6.18-rc4-mm1 (Andrew Morton's tree) is CONFIG_PCI_MULTITHREAD_PROBE.
This code was apparently never integrated into mainline. It appears to be superceded by the Asynchronous function calls work.