Hi, Jeremy
Since now the pv_ops domain0 is approaching, we are considering to port the
dom0 power management related code, or more specifically, the Cx/Px ACPI info
parsing code, to pv_ops domain0 tree, so that people can utilize Xen power
management capability (Cx/PX) under pv_ops domain0. This RFC is a draft version
for comments.
=== Overview ===
Requirement: Xen hypervisor need Cx/Px ACPI info to do the Cx/Px states power
management. This info is provided by BIOS ACPI table. Since hypervisor has no
ACPI parser, this info has to be parsed by domain0 kernel ACPI sub-system, and
then passed to hypervisor by hypercall.
To make this happen, the key point is to add hook in the kernel ACPI
sub-system. Fortunately, kernel already has good abstraction, and only several
places need to add hook. To be more detail, there is an acpi_processor_driver
(in drivers/acpi/processor_core.c) , which all the Cx/Px parsing event will go
to. This driver will call its acpi processor event handler, e.g. add/remove,
start/stop, notify to handle these events. These event handlers in turn will
call some library functions (in drivers/acpi/processor_perflib.c), e.g.
acpi_processor_ppc_has_changed, acpi_processor_ppc_has_changed,
acpi_processor_cst_has_changed, to finish the acpi info parsing.
So the conclusion is: adding hooks in acpi_processor_driver and those related
library functions will satisfy our requirement.
To make the added hook cleaner, we introduce an interface called external
control operation (struct processor_extcntl_ops). All the hooks are
encapsulated in this interface processor_extcntl_ops . Here the "external"
means the acpi processor is controlled by external entity, e.g. VMM. Every kind
of external entity can has its implementation of this interface. In this patch,
the interface for Xen is implemented.
== Patch Set Description ==
This patch set is based the xen/dom0/hackery branch. It has three patches:
1. acpi_parser_framework.patch
This patch introduces the interface of external control operation, and adds
hooks to the acpi sub-system, including the acpi_processor_driver, and the
related library functions.
2. acpi_parser_xen_driver.patch
This patch implements the Xen version of the external control operation
interface.
3. acpi_parser_platform_hypercall.patch
This patches implements the xen_platform_op hypercall, to pass the parsed ACPI
info to hypervisor.
== Misc ==
To make this patch works correctly, there is a corner case need to consider:
processor in domain0 is virtual CPU, while BIOS ACPI table provides the
physical CPU info, since the vCPU and pCPU is not 1:1 mapped, this may caused
unexpected result. E.g. in UP domain0, Xen hypervisor may only get one
physical processor info. Current linux-2.6.18-xen.hg tree solve this issue by
using acpi_id instead of processor_id. However, this code is a bit tricky and
hacky. We are still trying to find a cleaner way to solve this issue.
Comments are welcome.
Best Regards
Yu Ke and Tian Kevin
acpi_parser_framework.patch
Description: acpi_parser_framework.patch
acpi_parser_platform_hypercall.patch
Description: acpi_parser_platform_hypercall.patch
acpi_parser_xen_driver.patch
Description: acpi_parser_xen_driver.patch
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