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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2012-10-03 05:32:35 +0400 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-10-03 05:32:35 +0400 |
| commit | 16642a2e7be23bbda013fc32d8f6c68982eab603 (patch) | |
| tree | 346ae485f485f6901e5d8150f0d34d178a7dd448 /Documentation/cpu-freq/boost.txt | |
| parent | 51562cba98939da0a1d10fe7c25359b77a069033 (diff) | |
| parent | b9142167a2bb979b58b98ffcd928a311b55cbd9f (diff) | |
| download | linux-16642a2e7be23bbda013fc32d8f6c68982eab603.tar.xz | |
Merge tag 'pm-for-3.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
Pull power management updates from Rafael J Wysocki:
- Improved system suspend/resume and runtime PM handling for the SH
TMU, CMT and MTU2 clock event devices (also used by ARM/shmobile).
- Generic PM domains framework extensions related to cpuidle support
and domain objects lookup using names.
- ARM/shmobile power management updates including improved support for
the SH7372's A4S power domain containing the CPU core.
- cpufreq changes related to AMD CPUs support from Matthew Garrett,
Andre Przywara and Borislav Petkov.
- cpu0 cpufreq driver from Shawn Guo.
- cpufreq governor fixes related to the relaxing of limit from Michal
Pecio.
- OMAP cpufreq updates from Axel Lin and Richard Zhao.
- cpuidle ladder governor fixes related to the disabling of states from
Carsten Emde and me.
- Runtime PM core updates related to the interactions with the system
suspend core from Alan Stern and Kevin Hilman.
- Wakeup sources modification allowing more helper functions to be
called from interrupt context from John Stultz and additional
diagnostic code from Todd Poynor.
- System suspend error code path fix from Feng Hong.
Fixed up conflicts in cpufreq/powernow-k8 that stemmed from the
workqueue fixes conflicting fairly badly with the removal of support for
hardware P-state chips. The changes were independent but somewhat
intertwined.
* tag 'pm-for-3.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm: (76 commits)
Revert "PM QoS: Use spinlock in the per-device PM QoS constraints code"
PM / Runtime: let rpm_resume() succeed if RPM_ACTIVE, even when disabled, v2
cpuidle: rename function name "__cpuidle_register_driver", v2
cpufreq: OMAP: Check IS_ERR() instead of NULL for omap_device_get_by_hwmod_name
cpuidle: remove some empty lines
PM: Prevent runtime suspend during system resume
PM QoS: Use spinlock in the per-device PM QoS constraints code
PM / Sleep: use resume event when call dpm_resume_early
cpuidle / ACPI : move cpuidle_device field out of the acpi_processor_power structure
ACPI / processor: remove pointless variable initialization
ACPI / processor: remove unused function parameter
cpufreq: OMAP: remove loops_per_jiffy recalculate for smp
sections: fix section conflicts in drivers/cpufreq
cpufreq: conservative: update frequency when limits are relaxed
cpufreq / ondemand: update frequency when limits are relaxed
properly __init-annotate pm_sysrq_init()
cpufreq: Add a generic cpufreq-cpu0 driver
PM / OPP: Initialize OPP table from device tree
ARM: add cpufreq transiton notifier to adjust loops_per_jiffy for smp
cpufreq: Remove support for hardware P-state chips from powernow-k8
...
Diffstat (limited to 'Documentation/cpu-freq/boost.txt')
| -rw-r--r-- | Documentation/cpu-freq/boost.txt | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/Documentation/cpu-freq/boost.txt b/Documentation/cpu-freq/boost.txt new file mode 100644 index 000000000000..9b4edfcf486f --- /dev/null +++ b/Documentation/cpu-freq/boost.txt @@ -0,0 +1,93 @@ +Processor boosting control + + - information for users - + +Quick guide for the impatient: +-------------------- +/sys/devices/system/cpu/cpufreq/boost +controls the boost setting for the whole system. You can read and write +that file with either "0" (boosting disabled) or "1" (boosting allowed). +Reading or writing 1 does not mean that the system is boosting at this +very moment, but only that the CPU _may_ raise the frequency at it's +discretion. +-------------------- + +Introduction +------------- +Some CPUs support a functionality to raise the operating frequency of +some cores in a multi-core package if certain conditions apply, mostly +if the whole chip is not fully utilized and below it's intended thermal +budget. This is done without operating system control by a combination +of hardware and firmware. +On Intel CPUs this is called "Turbo Boost", AMD calls it "Turbo-Core", +in technical documentation "Core performance boost". In Linux we use +the term "boost" for convenience. + +Rationale for disable switch +---------------------------- + +Though the idea is to just give better performance without any user +intervention, sometimes the need arises to disable this functionality. +Most systems offer a switch in the (BIOS) firmware to disable the +functionality at all, but a more fine-grained and dynamic control would +be desirable: +1. While running benchmarks, reproducible results are important. Since + the boosting functionality depends on the load of the whole package, + single thread performance can vary. By explicitly disabling the boost + functionality at least for the benchmark's run-time the system will run + at a fixed frequency and results are reproducible again. +2. To examine the impact of the boosting functionality it is helpful + to do tests with and without boosting. +3. Boosting means overclocking the processor, though under controlled + conditions. By raising the frequency and the voltage the processor + will consume more power than without the boosting, which may be + undesirable for instance for mobile users. Disabling boosting may + save power here, though this depends on the workload. + + +User controlled switch +---------------------- + +To allow the user to toggle the boosting functionality, the acpi-cpufreq +driver exports a sysfs knob to disable it. There is a file: +/sys/devices/system/cpu/cpufreq/boost +which can either read "0" (boosting disabled) or "1" (boosting enabled). +Reading the file is always supported, even if the processor does not +support boosting. In this case the file will be read-only and always +reads as "0". Explicitly changing the permissions and writing to that +file anyway will return EINVAL. + +On supported CPUs one can write either a "0" or a "1" into this file. +This will either disable the boost functionality on all cores in the +whole system (0) or will allow the hardware to boost at will (1). + +Writing a "1" does not explicitly boost the system, but just allows the +CPU (and the firmware) to boost at their discretion. Some implementations +take external factors like the chip's temperature into account, so +boosting once does not necessarily mean that it will occur every time +even using the exact same software setup. + + +AMD legacy cpb switch +--------------------- +The AMD powernow-k8 driver used to support a very similar switch to +disable or enable the "Core Performance Boost" feature of some AMD CPUs. +This switch was instantiated in each CPU's cpufreq directory +(/sys/devices/system/cpu[0-9]*/cpufreq) and was called "cpb". +Though the per CPU existence hints at a more fine grained control, the +actual implementation only supported a system-global switch semantics, +which was simply reflected into each CPU's file. Writing a 0 or 1 into it +would pull the other CPUs to the same state. +For compatibility reasons this file and its behavior is still supported +on AMD CPUs, though it is now protected by a config switch +(X86_ACPI_CPUFREQ_CPB). On Intel CPUs this file will never be created, +even with the config option set. +This functionality is considered legacy and will be removed in some future +kernel version. + +More fine grained boosting control +---------------------------------- + +Technically it is possible to switch the boosting functionality at least +on a per package basis, for some CPUs even per core. Currently the driver +does not support it, but this may be implemented in the future. |