Low Power Idle Table (LPIT)¶
To enumerate platform Low Power Idle states, Intel platforms are using “Low Power Idle Table” (LPIT). More details about this table can be downloaded from: http://www.uefi.org/sites/default/files/resources/Intel_ACPI_Low_Power_S0_Idle.pdf
Residencies for each low power state can be read via FFH (Function fixed hardware) or a memory mapped interface.
On platforms supporting S0ix sleep states, there can be two types of residencies:
CPU PKG C10 (Read via FFH interface)
Platform Controller Hub (PCH) SLP_S0 (Read via memory mapped interface)
The following attributes are added dynamically to the cpuidle sysfs attribute group:
The "low_power_idle_cpu_residency_us" attribute shows time spent by the CPU package in PKG C10
The "low_power_idle_system_residency_us" attribute shows SLP_S0 residency, or system time spent with the SLP_S0# signal asserted. This is the lowest possible system power state, achieved only when CPU is in PKG C10 and all functional blocks in PCH are in a low power state.