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tools/power x86_energy_perf_policy.8: Emphasize preference for SW interfaces

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This tool was originally written when Linux had no standard
interface for EPB, or HWP support.

Retain the capability to manage a system w/o any kernel PM support,
but prefer the standard kernel interfaces, when avaialble.

(not doing so led to a confusing conflict between a p-state limit
 request made via cpufreq and modified by the intel-pstate driver,
 versus the raw MSR write made by this utility)

Signed-off-by: Len Brown <len.brown@intel.com>
This commit is contained in:
Len Brown
2025-09-24 11:50:29 -04:00
parent a648e0892c
commit 66f4305224
1 changed files with 11 additions and 4 deletions
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15
tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.8
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@@ -2,7 +2,7 @@
.\" Distributed under the GPL, Copyleft 1994.
.TH X86_ENERGY_PERF_POLICY 8
.SH NAME
x86_energy_perf_policy \- Manage Energy vs. Performance Policy via x86 Model Specific Registers
x86_energy_perf_policy \- Manage Energy vs. Performance Policy
.SH SYNOPSIS
.B x86_energy_perf_policy
.RB "[ options ] [ scope ] [field \ value]"
@@ -19,9 +19,14 @@ x86_energy_perf_policy \- Manage Energy vs. Performance Policy via x86 Model Spe
.SH DESCRIPTION
\fBx86_energy_perf_policy\fP
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.
Intel Architecture Processors. It summarizes settings available
in standard Linux interfaces (eg. cpufreq),
and also decodes underlying Model Specific Register (MSRs).
While \fBx86_energy_perf_policy\fP can manage energy-performance policy
using only MSR access, it prefers standard
Linux kernel interfaces, when they are available.
.SH BACKGROUND
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)
@@ -200,7 +205,9 @@ runs only as root.
.SH FILES
.ta
.nf
/dev/cpu/*/msr
EPB: /sys/devices/system/cpu/cpu*/power/energy_perf_bias
EPP: /sys/devices/system/cpu/cpu*/cpufreq/energy_performance_preference
MSR: /dev/cpu/*/msr
.fi
.SH "SEE ALSO"
.nf