Provided by: linux-tools-common_4.15.0-213.224_all 
NAME
x86_energy_perf_policy - Manage Energy vs. Performance Policy via x86 Model Specific
Registers
SYNOPSIS
x86_energy_perf_policy [ options ] [ scope ] [field value]
scope: --cpu cpu-list | --pkg pkg-list
cpu-list, pkg-list: # | #,# | #-# | all
field: --all | --epb | --hwp-epp | --hwp-min | --hwp-max | --hwp-desired
other: (--force | --hwp-enable | --turbo-enable) value)
value: # | default | performance | balance-performance | balance-power | power
DESCRIPTION
x86_energy_perf_policy displays and updates energy-performance policy settings specific to
Intel Architecture Processors. Settings are accessed via Model Specific Register (MSR)
updates, no matter if the Linux cpufreq sub-system is enabled or not.
Policy in MSR_IA32_ENERGY_PERF_BIAS (EPB) may affect a wide range of hardware decisions,
such as how aggressively the hardware enters and exits CPU idle states (C-states) and
Processor Performance States (P-states). This policy hint does not replace explicit OS C-
state and P-state selection. Rather, it tells the hardware how aggressively to implement
those selections. Further, it allows the OS to influence energy/performance trade-offs
where there is no software interface, such as in the opportunistic "turbo-mode" P-state
range. Note that MSR_IA32_ENERGY_PERF_BIAS is defined per CPU, but some implementations
share a single MSR among all CPUs in each processor package. On those systems, a write to
EPB on one processor will be visible, and will have an effect, on all CPUs in the same
processor package.
Hardware P-States (HWP) are effectively an expansion of hardware P-state control from the
opportunistic turbo-mode P-state range to include the entire range of available P-states.
On Broadwell Xeon, the initial HWP implementation, EBP influenced HWP. That influence was
removed in subsequent generations, where it was moved to the Energy_Performance_Preference
(EPP) field in a pair of dedicated MSRs -- MSR_IA32_HWP_REQUEST and
MSR_IA32_HWP_REQUEST_PKG.
EPP is the most commonly managed knob in HWP mode, but MSR_IA32_HWP_REQUEST also allows
the user to specify minimum-frequency for Quality-of-Service, and maximum-frequency for
power-capping. MSR_IA32_HWP_REQUEST is defined per-CPU.
MSR_IA32_HWP_REQUEST_PKG has the same capability as MSR_IA32_HWP_REQUEST, but it can
simultaneously set the default policy for all CPUs within a package. A bit in per-CPU
MSR_IA32_HWP_REQUEST indicates whether it is over-ruled-by or exempt-from
MSR_IA32_HWP_REQUEST_PKG.
MSR_HWP_CAPABILITIES shows the default values for the fields in MSR_IA32_HWP_REQUEST. It
is displayed when no values are being written.
SCOPE OPTIONS
-c, --cpu Operate on the MSR_IA32_HWP_REQUEST for each CPU in a CPU-list. The CPU-list
may be comma-separated CPU numbers, with dash for range or the string "all". Eg. '--cpu
1,4,6-8' or '--cpu all'. When --cpu is used, --hwp-use-pkg is available, which specifies
whether the per-cpu MSR_IA32_HWP_REQUEST should be over-ruled by MSR_IA32_HWP_REQUEST_PKG
(1), or exempt from MSR_IA32_HWP_REQUEST_PKG (0).
-p, --pkg Operate on the MSR_IA32_HWP_REQUEST_PKG for each package in the package-list.
The list is a string of individual package numbers separated by commas, and or ranges of
package numbers separated by a dash, or the string "all". For example '--pkg 1,3' or
'--pkg all'
VALUE OPTIONS
normal | default Set a policy with a normal balance between performance and energy
efficiency. The processor will tolerate minor performance compromise for potentially
significant energy savings. This is a reasonable default for most desktops and servers.
"default" is a synonym for "normal".
performance Set a policy for maximum performance, accepting no performance sacrifice for
the benefit of energy efficiency.
balance-performance Set a policy with a high priority on performance, but allowing some
performance loss to benefit energy efficiency.
balance-power Set a policy where the performance and power are balanced. This is the
default.
power Set a policy where the processor can accept a measurable performance impact to
maximize energy efficiency.
The following table shows the mapping from the value strings above to actual MSR values.
This mapping is defined in the Linux-kernel header, msr-index.h.
VALUE STRING EPB EPP
performance 0 0
balance-performance 4 128
normal, default 6 128
balance-power 8 192
power 15 255
For MSR_IA32_HWP_REQUEST performance fields (--hwp-min, --hwp-max, --hwp-desired), the
value option is in units of 100 MHz, Eg. 12 signifies 1200 MHz.
FIELD OPTIONS
-a, --all value-string Sets all EPB and EPP and HWP limit fields to the value associated
with the value-string. In addition, enables turbo-mode and HWP-mode, if they were
previous disabled. Thus "--all normal" will set a system without cpufreq into a well
known configuration.
-B, --epb set EPB per-core or per-package. See value strings in the table above.
-d, --debug debug increases verbosity. By default x86_energy_perf_policy is silent for
updates, and verbose for read-only mode.
-P, --hwp-epp set HWP.EPP per-core or per-package. See value strings in the table above.
-m, --hwp-min request HWP to not go below the specified core/bus ratio. The "default" is
the value found in IA32_HWP_CAPABILITIES.min.
-M, --hwp-max request HWP not exceed a the specified core/bus ratio. The "default" is the
value found in IA32_HWP_CAPABILITIES.max.
-D, --hwp-desired request HWP 'desired' frequency. The "normal" setting is 0, which
corresponds to 'full autonomous' HWP control. Non-zero performance values request a
specific performance level on this processor, specified in multiples of 100 MHz.
-w, --hwp-window specify integer number of microsec in the sliding window that HWP uses to
maintain average frequency. This parameter is meaningful only when the "desired" field
above is non-zero. Default is 0, allowing the HW to choose.
OTHER OPTIONS
-f, --force writes the specified values without bounds checking.
-U, --hwp-use-pkg (0 | 1), when used in conjunction with --cpu, indicates whether the per-
CPU MSR_IA32_HWP_REQUEST should be overruled (1) or exempt (0) from per-Package
MSR_IA32_HWP_REQUEST_PKG settings. The default is exempt.
-H, --hwp-enable enable HardWare-P-state (HWP) mode. Once enabled, system RESET is
required to disable HWP mode.
-t, --turbo-enable enable (1) or disable (0) turbo mode.
-v, --version print version and exit.
If no request to change policy is made, the default behavior is to read and display the
current system state, including the default capabilities.
WARNING
This utility writes directly to Model Specific Registers. There is no locking or
coordination should this utility be used to modify HWP limit fields at the same time that
intel_pstate's sysfs attributes access the same MSRs.
Note that --hwp-desired and --hwp-window are considered experimental. Future versions of
Linux reserve the right to access these fields internally -- potentially conflicting with
user-space access.
EXAMPLE
# sudo x86_energy_perf_policy
cpu0: EPB 6
cpu0: HWP_REQ: min 6 max 35 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0
cpu0: HWP_CAP: low 1 eff 8 guar 27 high 35
cpu1: EPB 6
cpu1: HWP_REQ: min 6 max 35 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0
cpu1: HWP_CAP: low 1 eff 8 guar 27 high 35
cpu2: EPB 6
cpu2: HWP_REQ: min 6 max 35 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0
cpu2: HWP_CAP: low 1 eff 8 guar 27 high 35
cpu3: EPB 6
cpu3: HWP_REQ: min 6 max 35 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0
cpu3: HWP_CAP: low 1 eff 8 guar 27 high 35
NOTES
x86_energy_perf_policy runs only as root.
FILES
/dev/cpu/*/msr
SEE ALSO
msr(4)
Intel(R) 64 and IA-32 Architectures Software Developer's Manual
AUTHORS
Len Brown
X86_ENERGY_PERF_POLICY(8)