15.1.6. Hotplug

CPU hotplug is a technique that can dynamically switch cores on or off. Hotplug can be used by the OSPM to change available compute capacity based on current compute requirements. Hotplug is also sometimes used for reliability reasons. There are a number of differences between hotplug and use of a power-down state for idle:

  1. When a core is hot unplugged, the supervisory software stops all use of that core in interrupt and thread processing. The core is no longer considered to be available by the calling OS.

  2. The OSPM has to issue an explicit command to bring a core back online, that is, hotplug a core. The appropriate supervisory software only starts scheduling on or enabling interrupts to that core after this command.

Operating systems typically perform much of the kernel boot process on one primary core, bringing secondary cores online at a later stage. Secondary boot behaves very similarly to hotplugging a core into the system. The operations in both cases are almost identical.

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