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Subject[PATCH v3 0/3] cpu: pseries: Cpu offline states framework

**** RFC not for inclusion ****

This is the version 3 of the patch series to provide a cpu-offline framework
that enables the administrators choose the state of a CPU when it is
offlined, when multiple such states are exposed by the underlying

Changes from Version 2:(can be found here:
- Addressed Andrew Morton's review comments regarding names of global
variables, handling of error conditions and documentation of the interfaces.

- Implemented a patch to provide helper functions to set the cede latency
specifier value in the VPA indicating latency expectation of the guest OS
when the vcpu is ceded from a subsequent H_CEDE hypercall. Hypervisor may
use this for better energy savings.

- Renamed of the cpu-hotplug states. "deallocate" is renamed
as "offline" and "deactivate" is renamed as "inactive".

The patch-series exposes the following sysfs tunables to
allow the system-adminstrator to choose the state of a CPU:

To query the available hotplug states, one needs to read the sysfs tunable:
To query or set the current state, on needs to read/write the sysfs tunable:

The patchset ensures that the writes to the "current_hotplug_state" sysfs file are
serialized against the writes to the "online" file.

This patchset contains the offline state driver implemented for
pSeries. For pSeries, we define three available_hotplug_states. They are:

online: The processor is online.

offline: This is the the default behaviour when the cpu is offlined
even in the absense of this driver. The CPU would call make an
rtas_stop_self() call and hand over the CPU back to the resource pool,
thereby effectively deallocating that vCPU from the LPAR.
NOTE: This would result in a configuration change to the LPAR
which is visible to the outside world.

inactive: This cedes the vCPU to the hypervisor with a cede latency
specifier value 2.
NOTE: This option does not result in a configuration change
and the vCPU would be still entitled to the LPAR to which it earlier
belong to.

Any feedback on the patchset will be immensely valuable.

Arun R Bharadwaj (1):
pSeries: cede latency specifier helper function.

Gautham R Shenoy (2):
cpu: Implement cpu-offline-state callbacks for pSeries.
cpu: Offline state Framework.

Documentation/cpu-hotplug.txt | 22 +++
arch/powerpc/include/asm/lppaca.h | 9 +
arch/powerpc/platforms/pseries/Makefile | 2
arch/powerpc/platforms/pseries/hotplug-cpu.c | 88 ++++++++++-
arch/powerpc/platforms/pseries/offline_driver.c | 148 +++++++++++++++++++
arch/powerpc/platforms/pseries/offline_driver.h | 20 +++
arch/powerpc/platforms/pseries/plpar_wrappers.h | 17 ++
arch/powerpc/platforms/pseries/smp.c | 17 ++
arch/powerpc/xmon/xmon.c | 3
drivers/base/cpu.c | 181 ++++++++++++++++++++++-
include/linux/cpu.h | 10 +
11 files changed, 498 insertions(+), 19 deletions(-)
create mode 100644 arch/powerpc/platforms/pseries/offline_driver.c
create mode 100644 arch/powerpc/platforms/pseries/offline_driver.h

Thanks and Regards

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