On 09/21/2013 06:15 AM, Zoran Markovic wrote:
This patch implements a generic CPU hotplug cooling device. The
implementation scales down the number of running CPUs when temperature
increases through a thermal trip point and prevents booting CPUs
until thermal conditions are restored. Upon restoration, the action
of starting up a CPU is left to another entity (e.g. CPU offline
governor, for which a patch is in the works).
In the past two years, ARM considerably reduced the time required for
CPUs to boot and shutdown; this time is now measured in microseconds.
This patch is predominantly intended for ARM big.LITTLE architectures
where big cores are expected to have a much bigger impact on thermal
budget than little cores, resulting in fast temperature ramps to a trip
point, i.e. thermal runaways. Switching off the big core(s) may be one
of the recovery mechanisms to restore system temperature, but the actual
strategy is left to the thermal governor.
The assumption is that CPU shutdown/startup is a rare event, so no
attempt was made to make the code atomic, i.e. the code evidently races
with CPU hotplug driver. The set_cur_state() function offlines CPUs
iteratively one at a time, checking the cooling state before each CPU
shutdown. A hotplug notifier callback validates any CPU boot requests
against current cooling state and approves/denies accordingly. This
mechanism guarantees that the desired cooling state could be reached in a
maximum of d-c iterations, where d and c are the "desired" and "current"
cooling states expressed in the number of offline CPUs.
Credits to Amit Daniel Kachhap for initial attempt to upstream this feature.
Cc: Zhang Rui<rui.zh...@intel.com>
Cc: Eduardo Valentin<eduardo.valen...@ti.com>
Cc: Rob Landley<r...@landley.net>
Cc: Amit Daniel Kachhap<amit.dan...@samsung.com>
Cc: Andrew Morton<a...@linux-foundation.org>
Cc: Durgadoss R<durgados...@intel.com>
Cc: Christian Daudt<b...@fixthebug.org>
Cc: James King<james.k...@linaro.org>
Signed-off-by: Zoran Markovic<zoran.marko...@linaro.org>
---
Documentation/thermal/cpu-cooling-api.txt | 17 ++
drivers/thermal/Kconfig | 10 +
drivers/thermal/Makefile | 1 +
drivers/thermal/cpu_hotplug.c | 362 +++++++++++++++++++++++++++++
include/linux/cpuhp_cooling.h | 57 +++++
5 files changed, 447 insertions(+)
create mode 100644 drivers/thermal/cpu_hotplug.c
create mode 100644 include/linux/cpuhp_cooling.h
Only form my point of view:
I like the name of cpu_hotplug_cooling.c and cpu_hotplug_cooling.h
we already have a cpu_cooling.c, that isn't so exact either because we
have more than one method to cool a CPU, these c and h files should be
renamed to cpu_freq_cooling.c and cpu_freq_cooling.h later.
By the way, some servers with tens of CPUs may need this patch too.
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