cpufreq: intel_pstate: Support for energy performance hints with HWP
It is possible to provide hints to the HWP algorithms in the processor
to be more performance centric to more energy centric. These hints are
provided by using HWP energy performance preference (EPP) or energy
performance bias (EPB) settings.
The scope of these settings is per logical processor, which means that
each of the logical processors in the package can be programmed with a
different value.
This change provides cpufreq sysfs interface to provide hint. For each
policy, two additional attributes will be available to check and provide
hint. These attributes will only be present when the intel_pstate driver
is using HWP mode.
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 changed via any method. User can
write any of the valid preference string to this attribute. User can
always restore to power-on default by writing "default".
Implementation
Since these hints can be provided by direct MSR write or using some tools
like x86_energy_perf_policy, the driver internally doesn't maintain any
state. The user operation will result in direct read/write of MSR: 0x774
(HWP_REQUEST_MSR). Also driver use read modify write to update other
fields in this MSR.
Summary of changes:
- struct cpudata field epp_saved is renamed to epp_powersave, as this
stores the value to restore once policy is switched from performance
to powersave to restore original powersave EPP value.
- A new struct cpudata field epp_saved is used to store the raw MSR
EPP/EPB value when a CPU goes offline or on suspend and restore on
online/resume. This ensures that EPP value is restored to correct
value irrespective of the means used to set.
- EPP/EPB value ranges are fixed for each preference, which can be
set for the cpufreq sysfs, so user request is mapped to/from this
range.
- New attributes are only added when HWP is present.
- Since EPP value of 0 is valid the fields are initialized to
-EINVAL when not valid. The field epp_default is read only once
after powerup to avoid reading on subsequent CPU online operation
- New suspend callback to store epp on suspend operation
- Don't invalidate old epp_saved field on resume and online as now
we can restore last epp value on suspend and this field can still
have old EPP value sampled during switch to performance from
powersave.
- While here optimized setting of cpu_data->epp_powersave = epp in
intel_pstate_hwp_set() as this was done in both true and false
paths.
- epp/epb set function returns error to caller on failure to pass
on to user space for display.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
1 file changed