50 lines
1.7 KiB
ReStructuredText
50 lines
1.7 KiB
ReStructuredText
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.. _pm_hld:
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Power Management
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################
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System PM module
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****************
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The PM module in the hypervisor does three things:
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- When all UOSes enter low power state, VM management will notify the SOS
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lifecycle service and trigger the SOS to enter a low-power state.
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SOS follows its own standard low-power state entry process and
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writes the ACPI control register to put SOS into low-power state.
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Hypervisor traps the ACPI control register writing and
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emulates SOS low-power state entry.
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- Once SOS low-power emulation is done, Hypervisor handles its
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own low-power state transition
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- Once system resumes from low-power mode, the hypervisor handles its
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own resume and emulates SOS resume too.
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It is assumed that SOS does not trigger any power state transition until
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the VM manager of ACRN notifies it that all UOSes are inactive and SOS
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offlines all its virtual APs.
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:numref:`pm-low-power-transition` shows the SOS/Hypervisor low-power
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state transition process. SOS triggers power state transition by
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writing ACPI control register on its virtual BSP (which is pinned to the
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physical BSP). The hypervisor then does the following in sequence before
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it writes to the physical ACPI control register to trigger physical
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power state transition:
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- Pauses SOS.
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- Offlines all physical APs.
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- Save the context of console, ioapic of SOS, I/O MMU, lapic of SOS,
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virtual BSP.
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- Save the context of physical BSP.
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When exiting from low-power mode, the hypervisor does similar steps in
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reverse order to restore contexts, start APs and resume SOS. SOS is
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responsible for starting its own virtual APs as well as UOSes.
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.. figure:: images/pm-image24-105.png
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:align: center
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:name: pm-low-power-transition
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SOS/Hypervisor low power state transition process
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