tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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1To enumerate platform Low Power Idle states, Intel platforms are using
2“Low Power Idle Table” (LPIT). More details about this table can be
3downloaded from:
4http://www.uefi.org/sites/default/files/resources/Intel_ACPI_Low_Power_S0_Idle.pdf
5
6Residencies for each low power state can be read via FFH
7(Function fixed hardware) or a memory mapped interface.
8
9On platforms supporting S0ix sleep states, there can be two types of
10residencies:
11- CPU PKG C10 (Read via FFH interface)
12- Platform Controller Hub (PCH) SLP_S0 (Read via memory mapped interface)
13
14The following attributes are added dynamically to the cpuidle
15sysfs attribute group:
16 /sys/devices/system/cpu/cpuidle/low_power_idle_cpu_residency_us
17 /sys/devices/system/cpu/cpuidle/low_power_idle_system_residency_us
18
19The "low_power_idle_cpu_residency_us" attribute shows time spent
20by the CPU package in PKG C10
21
22The "low_power_idle_system_residency_us" attribute shows SLP_S0
23residency, or system time spent with the SLP_S0# signal asserted.
24This is the lowest possible system power state, achieved only when CPU is in
25PKG C10 and all functional blocks in PCH are in a low power state.