1X86_ENERGY_PERF_POLICY(8) System Manager's Manual X86_ENERGY_PERF_POLICY(8)
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6 x86_energy_perf_policy - Manage Energy vs. Performance Policy via x86
7 Model Specific Registers
8
10 x86_energy_perf_policy [ options ] [ scope ] [field value]
11 scope: --cpu cpu-list | --pkg pkg-list
12 cpu-list, pkg-list: # | #,# | #-# | all
13 field: --all | --epb | --hwp-epp | --hwp-min | --hwp-max | --hwp-
14 desired
15 other: (--force | --hwp-enable | --turbo-enable) value)
16 value: # | default | performance | balance-performance | balance-power
17 | power
18
20 x86_energy_perf_policy displays and updates energy-performance policy
21 settings specific to Intel Architecture Processors. Settings are
22 accessed via Model Specific Register (MSR) updates, no matter if the
23 Linux cpufreq sub-system is enabled or not.
24 Policy in MSR_IA32_ENERGY_PERF_BIAS (EPB) may affect a wide range of
26 hardware decisions, such as how aggressively the hardware enters and
27 exits CPU idle states (C-states) and Processor Performance States (P-
28 states). This policy hint does not replace explicit OS C-state and P-
29 state selection. Rather, it tells the hardware how aggressively to
30 implement those selections. Further, it allows the OS to influence
31 energy/performance trade-offs where there is no software interface,
32 such as in the opportunistic "turbo-mode" P-state range. Note that
33 MSR_IA32_ENERGY_PERF_BIAS is defined per CPU, but some implementations
34 share a single MSR among all CPUs in each processor package. On those
35 systems, a write to EPB on one processor will be visible, and will have
36 an effect, on all CPUs in the same processor package.
37 Hardware P-States (HWP) are effectively an expansion of hardware P-
39 state control from the opportunistic turbo-mode P-state range to
40 include the entire range of available P-states. On Broadwell Xeon, the
41 initial HWP implementation, EBP influenced HWP. That influence was
42 removed in subsequent generations, where it was moved to the
43 Energy_Performance_Preference (EPP) field in a pair of dedicated MSRs
44 -- MSR_IA32_HWP_REQUEST and MSR_IA32_HWP_REQUEST_PKG.
45 EPP is the most commonly managed knob in HWP mode, but
47 MSR_IA32_HWP_REQUEST also allows the user to specify minimum-frequency
48 for Quality-of-Service, and maximum-frequency for power-capping.
49 MSR_IA32_HWP_REQUEST is defined per-CPU.
50 MSR_IA32_HWP_REQUEST_PKG has the same capability as
52 MSR_IA32_HWP_REQUEST, but it can simultaneously set the default policy
53 for all CPUs within a package. A bit in per-CPU MSR_IA32_HWP_REQUEST
54 indicates whether it is over-ruled-by or exempt-from
55 MSR_IA32_HWP_REQUEST_PKG.
56 MSR_HWP_CAPABILITIES shows the default values for the fields in
58 MSR_IA32_HWP_REQUEST. It is displayed when no values are being writ‐
59 ten.
60 SCOPE OPTIONS
63 -c, --cpu Operate on the MSR_IA32_HWP_REQUEST for each CPU in a CPU-
64 list. The CPU-list may be comma-separated CPU numbers, with dash for
65 range or the string "all". Eg. '--cpu 1,4,6-8' or '--cpu all'. When
66 --cpu is used, --hwp-use-pkg is available, which specifies whether the
67 per-cpu MSR_IA32_HWP_REQUEST should be over-ruled by
68 MSR_IA32_HWP_REQUEST_PKG (1), or exempt from MSR_IA32_HWP_REQUEST_PKG
69 (0).
70 -p, --pkg Operate on the MSR_IA32_HWP_REQUEST_PKG for each package in
72 the package-list. The list is a string of individual package numbers
73 separated by commas, and or ranges of package numbers separated by a
74 dash, or the string "all". For example '--pkg 1,3' or '--pkg all'
75 VALUE OPTIONS
78 normal | default Set a policy with a normal balance between performance
79 and energy efficiency. The processor will tolerate minor performance
80 compromise for potentially significant energy savings. This is a rea‐
81 sonable default for most desktops and servers. "default" is a synonym
82 for "normal".
83 performance Set a policy for maximum performance, accepting no perfor‐
85 mance sacrifice for the benefit of energy efficiency.
86 balance-performance Set a policy with a high priority on performance,
88 but allowing some performance loss to benefit energy efficiency.
89 balance-power Set a policy where the performance and power are bal‐
91 anced. This is the default.
92 power Set a policy where the processor can accept a measurable perfor‐
94 mance impact to maximize energy efficiency.
95 The following table shows the mapping from the value strings above to
98 actual MSR values. This mapping is defined in the Linux-kernel header,
99 msr-index.h.
100 VALUE STRING EPB EPP
102 performance 0 0
103 balance-performance 4 128
104 normal, default 6 128
105 balance-power 8 192
106 power 15 255
107 For MSR_IA32_HWP_REQUEST performance fields (--hwp-min, --hwp-max,
109 --hwp-desired), the value option is in units of 100 MHz, Eg. 12 signi‐
110 fies 1200 MHz.
111 FIELD OPTIONS
114 -a, --all value-string Sets all EPB and EPP and HWP limit fields to the
115 value associated with the value-string. In addition, enables turbo-
116 mode and HWP-mode, if they were previous disabled. Thus "--all normal"
117 will set a system without cpufreq into a well known configuration.
118 -B, --epb set EPB per-core or per-package. See value strings in the
120 table above.
121 -d, --debug debug increases verbosity. By default x86_energy_perf_pol‐
123 icy is silent for updates, and verbose for read-only mode.
124 -P, --hwp-epp set HWP.EPP per-core or per-package. See value strings
126 in the table above.
127 -m, --hwp-min request HWP to not go below the specified core/bus ratio.
129 The "default" is the value found in IA32_HWP_CAPABILITIES.min.
130 -M, --hwp-max request HWP not exceed a the specified core/bus ratio.
132 The "default" is the value found in IA32_HWP_CAPABILITIES.max.
133 -D, --hwp-desired request HWP 'desired' frequency. The "normal" set‐
135 ting is 0, which corresponds to 'full autonomous' HWP control. Non-
136 zero performance values request a specific performance level on this
137 processor, specified in multiples of 100 MHz.
138 -w, --hwp-window specify integer number of microsec in the sliding win‐
140 dow that HWP uses to maintain average frequency. This parameter is
141 meaningful only when the "desired" field above is non-zero. Default is
142 0, allowing the HW to choose.
143
145 -f, --force writes the specified values without bounds checking.
146 -U, --hwp-use-pkg (0 | 1), when used in conjunction with --cpu, indi‐
148 cates whether the per-CPU MSR_IA32_HWP_REQUEST should be overruled (1)
149 or exempt (0) from per-Package MSR_IA32_HWP_REQUEST_PKG settings. The
150 default is exempt.
151 -H, --hwp-enable enable HardWare-P-state (HWP) mode. Once enabled,
153 system RESET is required to disable HWP mode.
154 -t, --turbo-enable [22menable (1) or disable (0) turbo mode.
156 -v, --version print version and exit.
158 If no request to change policy is made, the default behavior is to read
160 and display the current system state, including the default capabili‐
161 ties.
162
164 This utility writes directly to Model Specific Registers. There is no
165 locking or coordination should this utility be used to modify HWP limit
166 fields at the same time that intel_pstate's sysfs attributes access the
167 same MSRs.
168 Note that --hwp-desired and --hwp-window are considered experimental.
170 Future versions of Linux reserve the right to access these fields
171 internally -- potentially conflicting with user-space access.
172
174 # sudo x86_energy_perf_policy
175 cpu0: EPB 6
176 cpu0: HWP_REQ: min 6 max 35 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0
177 cpu0: HWP_CAP: low 1 eff 8 guar 27 high 35
178 cpu1: EPB 6
179 cpu1: HWP_REQ: min 6 max 35 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0
180 cpu1: HWP_CAP: low 1 eff 8 guar 27 high 35
181 cpu2: EPB 6
182 cpu2: HWP_REQ: min 6 max 35 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0
183 cpu2: HWP_CAP: low 1 eff 8 guar 27 high 35
184 cpu3: EPB 6
185 cpu3: HWP_REQ: min 6 max 35 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0
186 cpu3: HWP_CAP: low 1 eff 8 guar 27 high 35
187
189 x86_energy_perf_policy runs only as root.
190
192 /dev/cpu/*/msr
193
195 msr(4)
196 Intel(R) 64 and IA-32 Architectures Software Developer's Manual
197
199 Len Brown
200 X86_ENERGY_PERF_POLICY(8)