1X86_ENERGY_PERF_POLICY(8)   System Manager's Manual  X86_ENERGY_PERF_POLICY(8)
2
3
4

NAME

6       x86_energy_perf_policy - read or write MSR_IA32_ENERGY_PERF_BIAS
7

SYNOPSIS

9       x86_energy_perf_policy [-c cpu] [-v] -r
10       x86_energy_perf_policy [-c cpu] [-v] 'performance'
11       x86_energy_perf_policy [-c cpu] [-v] 'normal'
12       x86_energy_perf_policy [-c cpu] [-v] 'powersave'
13       x86_energy_perf_policy [-c cpu] [-v] n
14

DESCRIPTION

16       x86_energy_perf_policy  allows  software  to  convey its policy for the
17       relative importance of performance versus energy savings to the proces‐
18       sor.
19
20       The processor uses this information in model-specific ways when it must
21       select trade-offs between performance and energy efficiency.
22
23       This policy hint does not supersede Processor  Performance  states  (P-
24       states)  or  CPU  Idle  power states (C-states), but allows software to
25       have influence where it would otherwise be unable to express a  prefer‐
26       ence.
27
28       For  example,  this  setting  may tell the hardware how aggressively or
29       conservatively to control frequency in  the  "turbo  range"  above  the
30       explicitly OS-controlled P-state frequency range.  It may also tell the
31       hardware how aggressively is should enter the OS requested C-states.
32
33       Support for this feature is indicated  by  CPUID.06H.ECX.bit3  per  the
34       Intel Architectures Software Developer's Manual.
35
36
37   Options
38       -c  limits operation to a single CPU.  The default is to operate on all
39       CPUs.  Note that MSR_IA32_ENERGY_PERF_BIAS is defined per logical  pro‐
40       cessor,  but  that  the  initial implementations of the MSR were shared
41       among all processors in each package.
42
43       -v increases verbosity.  By default x86_energy_perf_policy is silent.
44
45       -r is for "read-only" mode - the unchanged state is read and displayed.
46
47       performance Set a policy where performance is paramount.  The processor
48       will  be  unwilling to sacrifice any performance for the sake of energy
49       saving. This is the hardware default.
50
51       normal Set a policy with  a  normal  balance  between  performance  and
52       energy  efficiency.  The processor will tolerate minor performance com‐
53       promise for potentially significant energy  savings.   This  reasonable
54       default for most desktops and servers.
55
56       powersave Set a policy where the processor can accept a measurable per‐
57       formance hit to maximize energy efficiency.
58
59       n Set MSR_IA32_ENERGY_PERF_BIAS to the specified number.  The range  of
60       valid numbers is 0-15, where 0 is maximum performance and 15 is maximum
61       energy efficiency.
62
63

NOTES

65       x86_energy_perf_policy runs only as root.
66

FILES

68       /dev/cpu/*/msr
69
70

SEE ALSO

72       msr(4)
73

AUTHORS

75       Written by Len Brown <len.brown@intel.com>
76
77
78
79                                                     X86_ENERGY_PERF_POLICY(8)
Impressum