1 .. SPDX-License-Identifier: GPL-2.0
2
3 ==============================================
4 Legacy Documentation of CPU Performance Scalin
5 ==============================================
6
7 Included below are historic documents describi
8 :doc:`CPU performance scaling <cpufreq>` drive
9 with the original white space formatting and i
10 the added leading space character in every lin
11
12
13 AMD PowerNow! Drivers
14 =====================
15
16 ::
17
18 PowerNow! and Cool'n'Quiet are AMD names for
19 management capabilities in AMD processors. As
20 implementation changes in new generations of
21 there is a different cpu-freq driver for each
22
23 Note that the driver's will not load on the "
24 so it is safe to try each driver in turn when
25 which is the correct driver.
26
27 Note that the functionality to change frequen
28 is not available in all processors. The drive
29 to load on processors without this capability
30 is detected with the cpuid instruction.
31
32 The drivers use BIOS supplied tables to obtai
33 voltage information appropriate for a particu
34 Frequency transitions will be unavailable if
35 not supply these tables.
36
37 6th Generation: powernow-k6
38
39 7th Generation: powernow-k7: Athlon, Duron, G
40
41 8th Generation: powernow-k8: Athlon, Athlon 6
42 Documentation on this functionality in 8th ge
43 is available in the "BIOS and Kernel Develope
44 26094, in chapter 9, available for download f
45
46 BIOS supplied data, for powernow-k7 and for p
47 from either the PSB table or from ACPI object
48 is only available if the kernel config sets C
49 The powernow-k8 driver will attempt to use AC
50 and fall back to PST if that fails.
51 The powernow-k7 driver will try to use the PS
52 fall back to ACPI if the PSB support fails. A
53 acpi_force, is provided to force ACPI support
54 of PSB support.
55
56
57 ``cpufreq-nforce2``
58 ===================
59
60 ::
61
62 The cpufreq-nforce2 driver changes the FSB on
63
64 This works better than on other platforms, be
65 can be controlled independently from the PCI/
66
67 The module has two options:
68
69 fid: multiplier * 10 (for example
70 min_fsb: minimum FSB
71
72 If not set, fid is calculated from the curren
73 min_fsb defaults to FSB at boot time - 50 MHz
74
75 IMPORTANT: The available range is limited dow
76 Also the minimum available FSB can
77 booting with 200 MHz, 150 should a
78
79
80 ``pcc-cpufreq``
81 ===============
82
83 ::
84
85 /*
86 * pcc-cpufreq.txt - PCC interface documenta
87 *
88 * Copyright (C) 2009 Red Hat, Matthew Garre<
89 * Copyright (C) 2009 Hewlett-Packard Develo
90 * Nagananda Chumbalkar <nagananda.chumba
91 */
92
93
94 Processor Clocking Con
95 ----------------------
96
97 Contents:
98 ---------
99 1. Introduction
100 1.1 PCC interface
101 1.1.1 Get Average Frequency
102 1.1.2 Set Desired Frequency
103 1.2 Platforms affected
104 2. Driver and /sys details
105 2.1 scaling_available_frequencies
106 2.2 cpuinfo_transition_latency
107 2.3 cpuinfo_cur_freq
108 2.4 related_cpus
109 3. Caveats
110
111 1. Introduction:
112 ----------------
113 Processor Clocking Control (PCC) is an interf
114 firmware and OSPM. It is a mechanism for coor
115 performance (ie: frequency) between the platf
116
117 The PCC driver (pcc-cpufreq) allows OSPM to t
118 interface.
119
120 OS utilizes the PCC interface to inform platf
121 OS wants for a logical processor. The platfor
122 the requested frequency. If the request for t
123 satisfied by platform firmware, then it usual
124 conditions are in place, and "power capping"
125
126 1.1 PCC interface:
127 ------------------
128 The complete PCC specification is available h
129 https://acpica.org/sites/acpica/files/Process
130
131 PCC relies on a shared memory region that pro
132 between the OS and platform firmware. PCC als
133 is used by the OS to inform the platform firm
134 sent.
135
136 The ACPI PCCH() method is used to discover th
137 memory region. The shared memory region heade
138 "status" interface. PCCH() also contains deta
139 doorbell.
140
141 The following commands are supported by the P
142 * Get Average Frequency
143 * Set Desired Frequency
144
145 The ACPI PCCP() method is implemented for eac
146 used to discover the offsets for the input an
147 memory region.
148
149 When PCC mode is enabled, the platform will n
150 or throttle states (_PSS, _TSS and related AC
151 the native P-state driver (such as acpi-cpufr
152 AMD) will not load.
153
154 However, OSPM remains in control of policy. T
155 computes the required performance for each pr
156 The PCC driver fills in the command interface
157 communicates the request to the platform firm
158 responsible for delivering the requested perf
159
160 Each PCC command is "global" in scope and can
161 the system. Therefore, PCC is capable of perf
162 the OS is capable of getting/setting the freq
163 the system with a single call to the BIOS.
164
165 1.1.1 Get Average Frequency:
166 ----------------------------
167 This command is used by the OSPM to query the
168 processor since the last time this command wa
169 indicates the average unhalted frequency of t
170 a percentage of the nominal (ie: maximum) CPU
171 also signifies if the CPU frequency is limite
172
173 1.1.2 Set Desired Frequency:
174 ----------------------------
175 This command is used by the OSPM to communica
176 desired frequency for a logical processor. Th
177 ignored by OSPM. The next invocation of "Get
178 OSPM if the desired frequency was achieved or
179
180 1.2 Platforms affected:
181 -----------------------
182 The PCC driver will load on any system where
183 * supports the PCC interface, and the associa
184 * assumes responsibility for managing the har
185 to deliver the requested processor performanc
186
187 Currently, certain HP ProLiant platforms impl
188 platforms PCC is the "default" choice.
189
190 However, it is possible to disable this inter
191 such an instance, as is also the case on plat
192 is not implemented, the PCC driver will fail
193
194 2. Driver and /sys details:
195 ---------------------------
196 When the driver loads, it merely prints the l
197 frequencies supported by the platform firmwar
198
199 The PCC driver loads with a message such as:
200 pcc-cpufreq: (v1.00.00) driver loaded with fr
201 MHz
202
203 This means that the OPSM can request the CPU
204 between the limits (1600 MHz, and 2933 MHz) s
205
206 Internally, there is no need for the driver t
207 to a corresponding P-state.
208
209 The VERSION number for the driver will be of
210 eg: 1.00.02
211 ----- --
212 | |
213 | -- this will increase with bug fixes
214 |-- this is the version of the PCC specif
215
216
217 The following is a brief discussion on some o
218 /sys filesystem and how their values are affe
219
220 2.1 scaling_available_frequencies:
221 ----------------------------------
222 scaling_available_frequencies is not created
223 frequencies need to be listed because the BIO
224 frequency, within limits, requested by the go
225 to be strictly associated with a P-state.
226
227 2.2 cpuinfo_transition_latency:
228 -------------------------------
229 The cpuinfo_transition_latency field is 0. Th
230 not include a field to expose this value curr
231
232 2.3 cpuinfo_cur_freq:
233 ---------------------
234 A) Often cpuinfo_cur_freq will show a value d
235 in the scaling_available_frequencies or scali
236 This is due to "turbo boost" available on rec
237 conditions are met the BIOS can achieve a sli
238 by OSPM. An example:
239
240 scaling_cur_freq : 2933000
241 cpuinfo_cur_freq : 3196000
242
243 B) There is a round-off error associated with
244 Since the driver obtains the current frequenc
245 nominal frequency from the BIOS, sometimes, t
246 scaling_cur_freq and cpuinfo_cur_freq may not
247
248 scaling_cur_freq : 1600000
249 cpuinfo_cur_freq : 1583000
250
251 In this example, the nominal frequency is 293
252 current frequency, cpuinfo_cur_freq, as 54% o
253
254 54% of 2933 MHz = 1583 MHz
255
256 Nominal frequency is the maximum frequency of
257 corresponds to the frequency of the P0 P-stat
258
259 2.4 related_cpus:
260 -----------------
261 The related_cpus field is identical to affect
262
263 affected_cpus : 4
264 related_cpus : 4
265
266 Currently, the PCC driver does not evaluate _
267 PCC do not implement SW_ALL. So OSPM doesn't
268 to ensure that the same frequency is requeste
269
270 3. Caveats:
271 -----------
272 The "cpufreq_stats" module in its present for
273 expected to work with the PCC driver. Since t
274 provides information wrt each P-state, it is
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