105 lines
2.8 KiB
Groff
105 lines
2.8 KiB
Groff
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.\" This page Copyright (C) 2010 Len Brown <len.brown@intel.com>
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.\" Distributed under the GPL, Copyleft 1994.
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.TH X86_ENERGY_PERF_POLICY 8
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.SH NAME
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x86_energy_perf_policy \- read or write MSR_IA32_ENERGY_PERF_BIAS
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.SH SYNOPSIS
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.ft B
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.B x86_energy_perf_policy
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.RB [ "\-c cpu" ]
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.RB [ "\-v" ]
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.RB "\-r"
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.br
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.B x86_energy_perf_policy
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.RB [ "\-c cpu" ]
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.RB [ "\-v" ]
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.RB 'performance'
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.br
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.B x86_energy_perf_policy
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.RB [ "\-c cpu" ]
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.RB [ "\-v" ]
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.RB 'normal'
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.br
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.B x86_energy_perf_policy
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.RB [ "\-c cpu" ]
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.RB [ "\-v" ]
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.RB 'powersave'
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.br
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.B x86_energy_perf_policy
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.RB [ "\-c cpu" ]
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.RB [ "\-v" ]
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.RB n
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.br
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.SH DESCRIPTION
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\fBx86_energy_perf_policy\fP
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allows software to convey
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its policy for the relative importance of performance
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versus energy savings to the processor.
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The processor uses this information in model-specific ways
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when it must select trade-offs between performance and
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energy efficiency.
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This policy hint does not supersede Processor Performance states
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(P-states) or CPU Idle power states (C-states), but allows
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software to have influence where it would otherwise be unable
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to express a preference.
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For example, this setting may tell the hardware how
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aggressively or conservatively to control frequency
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in the "turbo range" above the explicitly OS-controlled
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P-state frequency range. It may also tell the hardware
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how aggressively is should enter the OS requested C-states.
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Support for this feature is indicated by CPUID.06H.ECX.bit3
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per the Intel Architectures Software Developer's Manual.
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.SS Options
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\fB-c\fP limits operation to a single CPU.
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The default is to operate on all CPUs.
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Note that MSR_IA32_ENERGY_PERF_BIAS is defined per
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logical processor, but that the initial implementations
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of the MSR were shared among all processors in each package.
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.PP
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\fB-v\fP increases verbosity. By default
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x86_energy_perf_policy is silent.
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.PP
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\fB-r\fP is for "read-only" mode - the unchanged state
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is read and displayed.
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.PP
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.I performance
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Set a policy where performance is paramount.
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The processor will be unwilling to sacrifice any performance
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for the sake of energy saving. This is the hardware default.
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.PP
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.I normal
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Set a policy with a normal balance between performance and energy efficiency.
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The processor will tolerate minor performance compromise
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for potentially significant energy savings.
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This reasonable default for most desktops and servers.
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.PP
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.I powersave
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Set a policy where the processor can accept
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a measurable performance hit to maximize energy efficiency.
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.PP
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.I n
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Set MSR_IA32_ENERGY_PERF_BIAS to the specified number.
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The range of valid numbers is 0-15, where 0 is maximum
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performance and 15 is maximum energy efficiency.
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.SH NOTES
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.B "x86_energy_perf_policy "
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runs only as root.
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.SH FILES
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.ta
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.nf
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/dev/cpu/*/msr
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.fi
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.SH "SEE ALSO"
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msr(4)
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.PP
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.SH AUTHORS
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.nf
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Written by Len Brown <len.brown@intel.com>
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