Xen Power Management

Support for Xilinx Zynq Ultrascale+ MPSoC

Presented to Xen ARM community on 8/2/2017

Power Management Design Overview

• Device management (EEMI)
• Device power states
• Resets
• MMIO access
• System management (PSCI/EEMI)
• Suspend
• Shutdown
• Restart
• CPU management (PSCI/EEMI)
• CPU hotplug
• CPU idle

EEMI - Embedded Energy Management Interface (Xilinx) https://www.xilinx.com/support/documentation/user_guides/ug1200-eemi-api.pdf

PSCI - Power State Coordination Interface (ARM) http://infocenter.arm.com/help/topic/com.arm.doc.den0022d/Power_State_Coordination_Interface_PDD_v1_1_DEN0022D.pdf

​

System Suspend Support

• Basic suspend scenario
• Each guest suspends on its own
• Linux/Dom0 suspends the last
• Xen suspends after all guests suspend
• Suspend consists of
• Suspending devices,
• Secondary cores using PSCI CPU_OFF and
• System using PSCI SYSTEM_SUSPEND
• Resume
• Always Dom0 + DomU depending on the wake source

System Management Coordination

How to enable Dom0 to trigger system wide suspend, shutdown, restart:

• Coordination needed to notify DomUs about desired operation
• EEMI interface includes callbacks for this purpose
• Xen paravirtualized callback interface for guest suspend and CPU hotplug
• Xenstore protocol (xlshutdown, etc)
• E.g. coordinated suspend scenario:
• System suspend initiated by Linux/Dom0
• Request DomUs to suspend (EEMI)
• Trigger init-suspend callbacks to DomUs (EEMI)
• After DomUs suspend Linux/Dom0 + Xen suspend as well

CPU Idle Support

• ACPI-based solution for x86 exists
• Existing ARM solution:
• Only standby (WFI) state is supported
• vPSCI CPU_SUSPEND is implemented (partially)
• Proposed ARM solution (PSCI-based):
• Goal is to support power-down of physical cores
• Required support for:
• CPU idle governor
• PSCI CPU_SUSPEND
• Suppressing ticks
• etc.