Let Sleeping CPUs Lie — S0ix Let Sleeping CPUs Lie — S0ix By Aymeric Wibo Modern laptops promise a kind of magic. Shut the lid or press the sleep button, toss it in a backpack, and hours, days, or weeks later, it should wake up as if nothing happened with little to no battery drain.

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A deep dive into the history and mechanics of CPU power management, from early SMM and APM to modern ACPI S0ix (suspend-to-idle) states. Explains why S3 sleep is being phased out in favor of S0ix on modern laptops, how S0ix works (device D-states, CPU C-states, s2idle loop), AMD-specific SMU/PMFW requirements, and the hybrid S0ix+hibernate approach. Covers the current state of FreeBSD's S0ix and hibernate implementation, including what works, what's still in progress, and which AMD chip families are supported.

Let Sleeping CPUs Lie — S0ix

History of Power Management, or: The Long Road to Doing Nothing Efficiently