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intel_pstate: Add support for HWP

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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>
This commit is contained in:
Dirk Brandewie
2014-11-06 09:40:47 -08:00
committed by Rafael J. Wysocki
parent 7787388772
commit 2f86dc4cdd
4 changed files with 165 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files
Documentation/cpu-freq/intel-pstate.txt
+23 -10
View File
@@ -1,17 +1,28 @@
Intel P-state driver
--------------------
This driver implements a scaling driver with an internal governor for
Intel Core processors. The driver follows the same model as the
Transmeta scaling driver (longrun.c) and implements the setpolicy()
instead of target(). Scaling drivers that implement setpolicy() are
assumed to implement internal governors by the cpufreq core. All the
logic for selecting the current P state is contained within the
driver; no external governor is used by the cpufreq core.
This driver provides an interface to control the P state selection for
SandyBridge+ Intel processors. The driver can operate two different
modes based on the processor model legacy and Hardware P state (HWP)
mode.
Intel SandyBridge+ processors are supported.
In legacy mode the driver implements a scaling driver with an internal
governor for Intel Core processors. The driver follows the same model
as the Transmeta scaling driver (longrun.c) and implements the
setpolicy() instead of target(). Scaling drivers that implement
setpolicy() are assumed to implement internal governors by the cpufreq
core. All the logic for selecting the current P state is contained
within the driver; no external governor is used by the cpufreq core.
New sysfs files for controlling P state selection have been added to
In HWP mode P state selection is implemented in the processor
itself. The driver provides the interfaces between the cpufreq core and
the processor to control P state selection based on user preferences
and reporting frequency to the cpufreq core. In this mode the
internal governor code is disabled.
In addtion to the interfaces provided by the cpufreq core for
controlling frequency the driver provides sysfs files for
controlling P state selection. These files have been added to
/sys/devices/system/cpu/intel_pstate/
max_perf_pct: limits the maximum P state that will be requested by
@@ -33,7 +44,9 @@ frequency is fiction 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.
New debugfs files have also been added to /sys/kernel/debug/pstate_snb/
For legacy mode debugfs files have also been added to allow tuning of
the internal governor algorythm. These files are located at
/sys/kernel/debug/pstate_snb/ These files are NOT present in HWP mode.
deadband
d_gain_pct