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Add support of Hardware Managed Performance States (HWP) described in Volume 3 section 14.4 of the SDM. With HWP enbaled intel_pstate will no longer be responsible for selecting P states for the processor. intel_pstate will continue to register to the cpufreq core as the scaling driver for CPUs implementing HWP. In HWP mode intel_pstate provides three functions reporting frequency to the cpufreq core, support for the set_policy() interface from the core and maintaining the intel_pstate sysfs interface in /sys/devices/system/cpu/intel_pstate. User preferences expressed via the set_policy() interface or the sysfs interface are forwared to the CPU via the HWP MSR interface. Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
57 lines
2.4 KiB
Plaintext
57 lines
2.4 KiB
Plaintext
Intel P-state driver
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--------------------
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This driver provides an interface to control the P state selection for
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SandyBridge+ Intel processors. The driver can operate two different
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modes based on the processor model legacy and Hardware P state (HWP)
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mode.
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In legacy mode the driver implements a scaling driver with an internal
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governor for Intel Core processors. The driver follows the same model
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as the Transmeta scaling driver (longrun.c) and implements the
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setpolicy() instead of target(). Scaling drivers that implement
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setpolicy() are assumed to implement internal governors by the cpufreq
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core. All the logic for selecting the current P state is contained
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within the driver; no external governor is used by the cpufreq core.
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In HWP mode P state selection is implemented in the processor
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itself. The driver provides the interfaces between the cpufreq core and
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the processor to control P state selection based on user preferences
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and reporting frequency to the cpufreq core. In this mode the
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internal governor code is disabled.
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In addtion to the interfaces provided by the cpufreq core for
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controlling frequency the driver provides sysfs files for
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controlling P state selection. These files have been added to
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/sys/devices/system/cpu/intel_pstate/
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max_perf_pct: limits the maximum P state that will be requested by
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the driver stated as a percentage of the available performance. The
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available (P states) performance may be reduced by the no_turbo
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setting described below.
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min_perf_pct: limits the minimum P state that will be requested by
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the driver stated as a percentage of the max (non-turbo)
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performance level.
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no_turbo: limits the driver to selecting P states below the turbo
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frequency range.
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For contemporary Intel processors, the frequency is controlled by the
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processor itself and the P-states exposed to software are related to
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performance levels. The idea that frequency can be set to a single
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frequency is fiction for Intel Core processors. Even if the scaling
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driver selects a single P state the actual frequency the processor
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will run at is selected by the processor itself.
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For legacy mode debugfs files have also been added to allow tuning of
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the internal governor algorythm. These files are located at
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/sys/kernel/debug/pstate_snb/ These files are NOT present in HWP mode.
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deadband
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d_gain_pct
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i_gain_pct
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p_gain_pct
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sample_rate_ms
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setpoint
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