Blame view

kernel/linux-rt-4.4.41/Documentation/cpu-freq/intel-pstate.txt 2.88 KB
5113f6f70   김현기   kernel add
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
  Intel P-state driver
  --------------------
  
  This driver provides an interface to control the P state selection for
  SandyBridge+ Intel processors.  The driver can operate two different
  modes based on the processor model, legacy mode and Hardware P state (HWP)
  mode.
  
  In legacy mode, the Intel P-state implements two internal governors,
  performance and powersave, that differ from the general cpufreq governors of
  the same name (the general cpufreq governors implement target(), whereas the
  internal Intel P-state governors implement setpolicy()).  The internal
  performance governor sets the max_perf_pct and min_perf_pct to 100; that is,
  the governor selects the highest available P state to maximize the performance
  of the core.  The internal powersave governor selects the appropriate P state
  based on the current load on the CPU.
  
  In HWP mode P state selection is implemented in the processor
  itself. The driver provides the interfaces between the cpufreq core and
  the processor to control P state selection based on user preferences
  and reporting frequency to the cpufreq core.  In this mode the
  internal Intel P-state governor code is disabled.
  
  In addition to the interfaces provided by the cpufreq core for
  controlling frequency the driver provides sysfs files for
  controlling P state selection. These files have been added to
  /sys/devices/system/cpu/intel_pstate/
  
        max_perf_pct: limits the maximum P state that will be requested by
        the driver stated as a percentage of the available performance. The
        available (P states) performance may be reduced by the no_turbo
        setting described below.
  
        min_perf_pct: limits the minimum P state that will be  requested by
        the driver stated as a percentage of the max (non-turbo)
        performance level.
  
        no_turbo: limits the driver to selecting P states below the turbo
        frequency range.
  
        turbo_pct: displays the percentage of the total performance that
        is supported by hardware that is in the turbo range.  This number
        is independent of whether turbo has been disabled or not.
  
        num_pstates: displays the number of pstates that are supported
        by hardware.  This number is independent of whether turbo has
        been disabled or not.
  
  For contemporary Intel processors, the frequency is controlled by the
  processor itself and the P-states exposed to software are related to
  performance levels.  The idea that frequency can be set to a single
  frequency is fiction for Intel Core processors. Even if the scaling
  driver selects a single P state the actual frequency the processor
  will run at is selected by the processor itself.
  
  For legacy mode debugfs files have also been added to allow tuning of
  the internal governor algorythm. These files are located at
  /sys/kernel/debug/pstate_snb/ These files are NOT present in HWP mode.
  
        deadband
        d_gain_pct
        i_gain_pct
        p_gain_pct
        sample_rate_ms
        setpoint