Intel Driver Works On "PM Suspend Freeze" Support
Zhang Rui of Intel is working on supporting the PM_SUSPEND_FREEZE power management suspend state for their open-source Linux graphics driver. This PM suspend state has some benefits over other current power states but also some shortcomings.
PM_SUSPEND_FREEZE doesn't depend upon any platform specific support but is a state whereby processes are frozen, devices suspended, and processors idled. PM_SUSPEND_FREEZE saves less power than PM_SUSPEND_MEMORY as the system is still in a running state, but it has shorter resume latency since it doesn't touch the BIOS and the processors are sitting in an idled state.
Compared to RTPM/idle, Zhang Rui says PM_SUSPEND_FREEZE has greater power savings as the processors have longer sleep time and the CPUs can drop into deeper C-states. PM_SUSPEND_FREEZE also uses the system suspend code path so there's greater power savings from hardware that lacks good RTPM support.
The PM suspend freeze state is characterized as good for platforms without (or broken) STR or where the hardware has an extremely low-power idle state.
More information and early tests on PM_SUSPEND_FREEZE when supported by the open-source Intel Linux graphics driver can be found on the intel-gfx mailing list. The initial results contain average power consumption results under different power management states as well as the average resume latency from these different states.
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