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Diffstat (limited to 'Documentation/cpu-freq/intel-pstate.txt')
| -rw-r--r-- | Documentation/cpu-freq/intel-pstate.txt | 69 |
1 files changed, 64 insertions, 5 deletions
diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt index e6bd1e6512a5..3fdcdfd968ba 100644 --- a/Documentation/cpu-freq/intel-pstate.txt +++ b/Documentation/cpu-freq/intel-pstate.txt @@ -48,7 +48,7 @@ In addition to the frequency-controlling interfaces provided by the cpufreq core, the driver provides its own sysfs files to control the P-State selection. These files have been added to /sys/devices/system/cpu/intel_pstate/. Any changes made to these files are applicable to all CPUs (even in a -multi-package system). +multi-package system, Refer to later section on placing "Per-CPU limits"). max_perf_pct: Limits the maximum P-State that will be requested by the driver. It states it as a percentage of the available performance. The @@ -85,6 +85,21 @@ Sysfs will show : Refer to "Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 3: System Programming Guide" to understand ratios. +There is one more sysfs attribute in /sys/devices/system/cpu/intel_pstate/ +that can be used for controlling the operation mode of the driver: + + status: Three settings are possible: + "off" - The driver is not in use at this time. + "active" - The driver works as a P-state governor (default). + "passive" - The driver works as a regular cpufreq one and collaborates + with the generic cpufreq governors (it sets P-states as + requested by those governors). + The current setting is returned by reads from this attribute. Writing one + of the above strings to it changes the operation mode as indicated by that + string, if possible. If HW-managed P-states (HWP) are enabled, it is not + possible to change the driver's operation mode and attempts to write to + this attribute will fail. + cpufreq sysfs for Intel P-State Since this driver registers with cpufreq, cpufreq sysfs is also presented. @@ -120,13 +135,57 @@ frequency is fictional for Intel Core processors. Even if the scaling driver selects a single P-State, the actual frequency the processor will run at is selected by the processor itself. +Per-CPU limits + +The kernel command line option "intel_pstate=per_cpu_perf_limits" forces +the intel_pstate driver to use per-CPU performance limits. When it is set, +the sysfs control interface described above is subject to limitations. +- The following controls are not available for both read and write + /sys/devices/system/cpu/intel_pstate/max_perf_pct + /sys/devices/system/cpu/intel_pstate/min_perf_pct +- The following controls can be used to set performance limits, as far as the +architecture of the processor permits: + /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq + /sys/devices/system/cpu/cpu*/cpufreq/scaling_min_freq + /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor +- User can still observe turbo percent and number of P-States from + /sys/devices/system/cpu/intel_pstate/turbo_pct + /sys/devices/system/cpu/intel_pstate/num_pstates +- User can read write system wide turbo status + /sys/devices/system/cpu/no_turbo + +Support of energy performance hints +It is possible to provide hints to the HWP algorithms in the processor +to be more performance centric to more energy centric. When the driver +is using HWP, two additional cpufreq sysfs attributes are presented for +each logical CPU. +These attributes are: + - energy_performance_available_preferences + - energy_performance_preference + +To get list of supported hints: +$ cat energy_performance_available_preferences + default performance balance_performance balance_power power + +The current preference can be read or changed via cpufreq sysfs +attribute "energy_performance_preference". Reading from this attribute +will display current effective setting. User can write any of the valid +preference string to this attribute. User can always restore to power-on +default by writing "default". + +Since threads can migrate to different CPUs, this is possible that the +new CPU may have different energy performance preference than the previous +one. To avoid such issues, either threads can be pinned to specific CPUs +or set the same energy performance preference value to all CPUs. + Tuning Intel P-State driver -When HWP mode is not used, debugfs files have also been added to allow the -tuning of the internal governor algorithm. These files are located at -/sys/kernel/debug/pstate_snb/. The algorithm uses a PID (Proportional -Integral Derivative) controller. The PID tunable parameters are: +When the performance can be tuned using PID (Proportional Integral +Derivative) controller, debugfs files are provided for adjusting performance. +They are presented under: +/sys/kernel/debug/pstate_snb/ +The PID tunable parameters are: deadband d_gain_pct i_gain_pct |