1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 ============================================== 3 =======================================================
4 Legacy Documentation of CPU Performance Scalin 4 Legacy Documentation of CPU Performance Scaling Drivers
5 ============================================== 5 =======================================================
6 6
7 Included below are historic documents describi 7 Included below are historic documents describing assorted
8 :doc:`CPU performance scaling <cpufreq>` drive 8 :doc:`CPU performance scaling <cpufreq>` drivers. They are reproduced verbatim,
9 with the original white space formatting and i 9 with the original white space formatting and indentation preserved, except for
10 the added leading space character in every lin 10 the added leading space character in every line of text.
11 11
12 12
13 AMD PowerNow! Drivers 13 AMD PowerNow! Drivers
14 ===================== 14 =====================
15 15
16 :: 16 ::
17 17
18 PowerNow! and Cool'n'Quiet are AMD names for 18 PowerNow! and Cool'n'Quiet are AMD names for frequency
19 management capabilities in AMD processors. As 19 management capabilities in AMD processors. As the hardware
20 implementation changes in new generations of 20 implementation changes in new generations of the processors,
21 there is a different cpu-freq driver for each 21 there is a different cpu-freq driver for each generation.
22 22
23 Note that the driver's will not load on the " 23 Note that the driver's will not load on the "wrong" hardware,
24 so it is safe to try each driver in turn when 24 so it is safe to try each driver in turn when in doubt as to
25 which is the correct driver. 25 which is the correct driver.
26 26
27 Note that the functionality to change frequen 27 Note that the functionality to change frequency (and voltage)
28 is not available in all processors. The drive 28 is not available in all processors. The drivers will refuse
29 to load on processors without this capability 29 to load on processors without this capability. The capability
30 is detected with the cpuid instruction. 30 is detected with the cpuid instruction.
31 31
32 The drivers use BIOS supplied tables to obtai 32 The drivers use BIOS supplied tables to obtain frequency and
33 voltage information appropriate for a particu 33 voltage information appropriate for a particular platform.
34 Frequency transitions will be unavailable if 34 Frequency transitions will be unavailable if the BIOS does
35 not supply these tables. 35 not supply these tables.
36 36
37 6th Generation: powernow-k6 37 6th Generation: powernow-k6
38 38
39 7th Generation: powernow-k7: Athlon, Duron, G 39 7th Generation: powernow-k7: Athlon, Duron, Geode.
40 40
41 8th Generation: powernow-k8: Athlon, Athlon 6 41 8th Generation: powernow-k8: Athlon, Athlon 64, Opteron, Sempron.
42 Documentation on this functionality in 8th ge 42 Documentation on this functionality in 8th generation processors
43 is available in the "BIOS and Kernel Develope 43 is available in the "BIOS and Kernel Developer's Guide", publication
44 26094, in chapter 9, available for download f 44 26094, in chapter 9, available for download from www.amd.com.
45 45
46 BIOS supplied data, for powernow-k7 and for p 46 BIOS supplied data, for powernow-k7 and for powernow-k8, may be
47 from either the PSB table or from ACPI object 47 from either the PSB table or from ACPI objects. The ACPI support
48 is only available if the kernel config sets C 48 is only available if the kernel config sets CONFIG_ACPI_PROCESSOR.
49 The powernow-k8 driver will attempt to use AC 49 The powernow-k8 driver will attempt to use ACPI if so configured,
50 and fall back to PST if that fails. 50 and fall back to PST if that fails.
51 The powernow-k7 driver will try to use the PS 51 The powernow-k7 driver will try to use the PSB support first, and
52 fall back to ACPI if the PSB support fails. A 52 fall back to ACPI if the PSB support fails. A module parameter,
53 acpi_force, is provided to force ACPI support 53 acpi_force, is provided to force ACPI support to be used instead
54 of PSB support. 54 of PSB support.
55 55
56 56
57 ``cpufreq-nforce2`` 57 ``cpufreq-nforce2``
58 =================== 58 ===================
59 59
60 :: 60 ::
61 61
62 The cpufreq-nforce2 driver changes the FSB on 62 The cpufreq-nforce2 driver changes the FSB on nVidia nForce2 platforms.
63 63
64 This works better than on other platforms, be 64 This works better than on other platforms, because the FSB of the CPU
65 can be controlled independently from the PCI/ 65 can be controlled independently from the PCI/AGP clock.
66 66
67 The module has two options: 67 The module has two options:
68 68
69 fid: multiplier * 10 (for example 69 fid: multiplier * 10 (for example 8.5 = 85)
70 min_fsb: minimum FSB 70 min_fsb: minimum FSB
71 71
72 If not set, fid is calculated from the curren 72 If not set, fid is calculated from the current CPU speed and the FSB.
73 min_fsb defaults to FSB at boot time - 50 MHz 73 min_fsb defaults to FSB at boot time - 50 MHz.
74 74
75 IMPORTANT: The available range is limited dow 75 IMPORTANT: The available range is limited downwards!
76 Also the minimum available FSB can 76 Also the minimum available FSB can differ, for systems
77 booting with 200 MHz, 150 should a 77 booting with 200 MHz, 150 should always work.
78 78
79 79
80 ``pcc-cpufreq`` 80 ``pcc-cpufreq``
81 =============== 81 ===============
82 82
83 :: 83 ::
84 84
85 /* 85 /*
86 * pcc-cpufreq.txt - PCC interface documenta 86 * pcc-cpufreq.txt - PCC interface documentation
87 * 87 *
88 * Copyright (C) 2009 Red Hat, Matthew Garre< 88 * Copyright (C) 2009 Red Hat, Matthew Garrett <mjg@redhat.com>
89 * Copyright (C) 2009 Hewlett-Packard Develo 89 * Copyright (C) 2009 Hewlett-Packard Development Company, L.P.
90 * Nagananda Chumbalkar <nagananda.chumba 90 * Nagananda Chumbalkar <nagananda.chumbalkar@hp.com>
91 */ 91 */
92 92
93 93
94 Processor Clocking Con 94 Processor Clocking Control Driver
95 ---------------------- 95 ---------------------------------
96 96
97 Contents: 97 Contents:
98 --------- 98 ---------
99 1. Introduction 99 1. Introduction
100 1.1 PCC interface 100 1.1 PCC interface
101 1.1.1 Get Average Frequency 101 1.1.1 Get Average Frequency
102 1.1.2 Set Desired Frequency 102 1.1.2 Set Desired Frequency
103 1.2 Platforms affected 103 1.2 Platforms affected
104 2. Driver and /sys details 104 2. Driver and /sys details
105 2.1 scaling_available_frequencies 105 2.1 scaling_available_frequencies
106 2.2 cpuinfo_transition_latency 106 2.2 cpuinfo_transition_latency
107 2.3 cpuinfo_cur_freq 107 2.3 cpuinfo_cur_freq
108 2.4 related_cpus 108 2.4 related_cpus
109 3. Caveats 109 3. Caveats
110 110
111 1. Introduction: 111 1. Introduction:
112 ---------------- 112 ----------------
113 Processor Clocking Control (PCC) is an interf 113 Processor Clocking Control (PCC) is an interface between the platform
114 firmware and OSPM. It is a mechanism for coor 114 firmware and OSPM. It is a mechanism for coordinating processor
115 performance (ie: frequency) between the platf 115 performance (ie: frequency) between the platform firmware and the OS.
116 116
117 The PCC driver (pcc-cpufreq) allows OSPM to t 117 The PCC driver (pcc-cpufreq) allows OSPM to take advantage of the PCC
118 interface. 118 interface.
119 119
120 OS utilizes the PCC interface to inform platf 120 OS utilizes the PCC interface to inform platform firmware what frequency the
121 OS wants for a logical processor. The platfor 121 OS wants for a logical processor. The platform firmware attempts to achieve
122 the requested frequency. If the request for t 122 the requested frequency. If the request for the target frequency could not be
123 satisfied by platform firmware, then it usual 123 satisfied by platform firmware, then it usually means that power budget
124 conditions are in place, and "power capping" 124 conditions are in place, and "power capping" is taking place.
125 125
126 1.1 PCC interface: 126 1.1 PCC interface:
127 ------------------ 127 ------------------
128 The complete PCC specification is available h 128 The complete PCC specification is available here:
129 https://acpica.org/sites/acpica/files/Process 129 https://acpica.org/sites/acpica/files/Processor-Clocking-Control-v1p0.pdf
130 130
131 PCC relies on a shared memory region that pro 131 PCC relies on a shared memory region that provides a channel for communication
132 between the OS and platform firmware. PCC als 132 between the OS and platform firmware. PCC also implements a "doorbell" that
133 is used by the OS to inform the platform firm 133 is used by the OS to inform the platform firmware that a command has been
134 sent. 134 sent.
135 135
136 The ACPI PCCH() method is used to discover th 136 The ACPI PCCH() method is used to discover the location of the PCC shared
137 memory region. The shared memory region heade 137 memory region. The shared memory region header contains the "command" and
138 "status" interface. PCCH() also contains deta 138 "status" interface. PCCH() also contains details on how to access the platform
139 doorbell. 139 doorbell.
140 140
141 The following commands are supported by the P 141 The following commands are supported by the PCC interface:
142 * Get Average Frequency 142 * Get Average Frequency
143 * Set Desired Frequency 143 * Set Desired Frequency
144 144
145 The ACPI PCCP() method is implemented for eac 145 The ACPI PCCP() method is implemented for each logical processor and is
146 used to discover the offsets for the input an 146 used to discover the offsets for the input and output buffers in the shared
147 memory region. 147 memory region.
148 148
149 When PCC mode is enabled, the platform will n 149 When PCC mode is enabled, the platform will not expose processor performance
150 or throttle states (_PSS, _TSS and related AC 150 or throttle states (_PSS, _TSS and related ACPI objects) to OSPM. Therefore,
151 the native P-state driver (such as acpi-cpufr 151 the native P-state driver (such as acpi-cpufreq for Intel, powernow-k8 for
152 AMD) will not load. 152 AMD) will not load.
153 153
154 However, OSPM remains in control of policy. T 154 However, OSPM remains in control of policy. The governor (eg: "ondemand")
155 computes the required performance for each pr 155 computes the required performance for each processor based on server workload.
156 The PCC driver fills in the command interface 156 The PCC driver fills in the command interface, and the input buffer and
157 communicates the request to the platform firm 157 communicates the request to the platform firmware. The platform firmware is
158 responsible for delivering the requested perf 158 responsible for delivering the requested performance.
159 159
160 Each PCC command is "global" in scope and can 160 Each PCC command is "global" in scope and can affect all the logical CPUs in
161 the system. Therefore, PCC is capable of perf 161 the system. Therefore, PCC is capable of performing "group" updates. With PCC
162 the OS is capable of getting/setting the freq 162 the OS is capable of getting/setting the frequency of all the logical CPUs in
163 the system with a single call to the BIOS. 163 the system with a single call to the BIOS.
164 164
165 1.1.1 Get Average Frequency: 165 1.1.1 Get Average Frequency:
166 ---------------------------- 166 ----------------------------
167 This command is used by the OSPM to query the 167 This command is used by the OSPM to query the running frequency of the
168 processor since the last time this command wa 168 processor since the last time this command was completed. The output buffer
169 indicates the average unhalted frequency of t 169 indicates the average unhalted frequency of the logical processor expressed as
170 a percentage of the nominal (ie: maximum) CPU 170 a percentage of the nominal (ie: maximum) CPU frequency. The output buffer
171 also signifies if the CPU frequency is limite 171 also signifies if the CPU frequency is limited by a power budget condition.
172 172
173 1.1.2 Set Desired Frequency: 173 1.1.2 Set Desired Frequency:
174 ---------------------------- 174 ----------------------------
175 This command is used by the OSPM to communica 175 This command is used by the OSPM to communicate to the platform firmware the
176 desired frequency for a logical processor. Th 176 desired frequency for a logical processor. The output buffer is currently
177 ignored by OSPM. The next invocation of "Get 177 ignored by OSPM. The next invocation of "Get Average Frequency" will inform
178 OSPM if the desired frequency was achieved or 178 OSPM if the desired frequency was achieved or not.
179 179
180 1.2 Platforms affected: 180 1.2 Platforms affected:
181 ----------------------- 181 -----------------------
182 The PCC driver will load on any system where 182 The PCC driver will load on any system where the platform firmware:
183 * supports the PCC interface, and the associa 183 * supports the PCC interface, and the associated PCCH() and PCCP() methods
184 * assumes responsibility for managing the har 184 * assumes responsibility for managing the hardware clocking controls in order
185 to deliver the requested processor performanc 185 to deliver the requested processor performance
186 186
187 Currently, certain HP ProLiant platforms impl 187 Currently, certain HP ProLiant platforms implement the PCC interface. On those
188 platforms PCC is the "default" choice. 188 platforms PCC is the "default" choice.
189 189
190 However, it is possible to disable this inter 190 However, it is possible to disable this interface via a BIOS setting. In
191 such an instance, as is also the case on plat 191 such an instance, as is also the case on platforms where the PCC interface
192 is not implemented, the PCC driver will fail 192 is not implemented, the PCC driver will fail to load silently.
193 193
194 2. Driver and /sys details: 194 2. Driver and /sys details:
195 --------------------------- 195 ---------------------------
196 When the driver loads, it merely prints the l 196 When the driver loads, it merely prints the lowest and the highest CPU
197 frequencies supported by the platform firmwar 197 frequencies supported by the platform firmware.
198 198
199 The PCC driver loads with a message such as: 199 The PCC driver loads with a message such as:
200 pcc-cpufreq: (v1.00.00) driver loaded with fr 200 pcc-cpufreq: (v1.00.00) driver loaded with frequency limits: 1600 MHz, 2933
201 MHz 201 MHz
202 202
203 This means that the OPSM can request the CPU 203 This means that the OPSM can request the CPU to run at any frequency in
204 between the limits (1600 MHz, and 2933 MHz) s 204 between the limits (1600 MHz, and 2933 MHz) specified in the message.
205 205
206 Internally, there is no need for the driver t 206 Internally, there is no need for the driver to convert the "target" frequency
207 to a corresponding P-state. 207 to a corresponding P-state.
208 208
209 The VERSION number for the driver will be of 209 The VERSION number for the driver will be of the format v.xy.ab.
210 eg: 1.00.02 210 eg: 1.00.02
211 ----- -- 211 ----- --
212 | | 212 | |
213 | -- this will increase with bug fixes 213 | -- this will increase with bug fixes/enhancements to the driver
214 |-- this is the version of the PCC specif 214 |-- this is the version of the PCC specification the driver adheres to
215 215
216 216
217 The following is a brief discussion on some o 217 The following is a brief discussion on some of the fields exported via the
218 /sys filesystem and how their values are affe 218 /sys filesystem and how their values are affected by the PCC driver:
219 219
220 2.1 scaling_available_frequencies: 220 2.1 scaling_available_frequencies:
221 ---------------------------------- 221 ----------------------------------
222 scaling_available_frequencies is not created 222 scaling_available_frequencies is not created in /sys. No intermediate
223 frequencies need to be listed because the BIO 223 frequencies need to be listed because the BIOS will try to achieve any
224 frequency, within limits, requested by the go 224 frequency, within limits, requested by the governor. A frequency does not have
225 to be strictly associated with a P-state. 225 to be strictly associated with a P-state.
226 226
227 2.2 cpuinfo_transition_latency: 227 2.2 cpuinfo_transition_latency:
228 ------------------------------- 228 -------------------------------
229 The cpuinfo_transition_latency field is 0. Th 229 The cpuinfo_transition_latency field is 0. The PCC specification does
230 not include a field to expose this value curr 230 not include a field to expose this value currently.
231 231
232 2.3 cpuinfo_cur_freq: 232 2.3 cpuinfo_cur_freq:
233 --------------------- 233 ---------------------
234 A) Often cpuinfo_cur_freq will show a value d 234 A) Often cpuinfo_cur_freq will show a value different than what is declared
235 in the scaling_available_frequencies or scali 235 in the scaling_available_frequencies or scaling_cur_freq, or scaling_max_freq.
236 This is due to "turbo boost" available on rec 236 This is due to "turbo boost" available on recent Intel processors. If certain
237 conditions are met the BIOS can achieve a sli 237 conditions are met the BIOS can achieve a slightly higher speed than requested
238 by OSPM. An example: 238 by OSPM. An example:
239 239
240 scaling_cur_freq : 2933000 240 scaling_cur_freq : 2933000
241 cpuinfo_cur_freq : 3196000 241 cpuinfo_cur_freq : 3196000
242 242
243 B) There is a round-off error associated with 243 B) There is a round-off error associated with the cpuinfo_cur_freq value.
244 Since the driver obtains the current frequenc 244 Since the driver obtains the current frequency as a "percentage" (%) of the
245 nominal frequency from the BIOS, sometimes, t 245 nominal frequency from the BIOS, sometimes, the values displayed by
246 scaling_cur_freq and cpuinfo_cur_freq may not 246 scaling_cur_freq and cpuinfo_cur_freq may not match. An example:
247 247
248 scaling_cur_freq : 1600000 248 scaling_cur_freq : 1600000
249 cpuinfo_cur_freq : 1583000 249 cpuinfo_cur_freq : 1583000
250 250
251 In this example, the nominal frequency is 293 251 In this example, the nominal frequency is 2933 MHz. The driver obtains the
252 current frequency, cpuinfo_cur_freq, as 54% o 252 current frequency, cpuinfo_cur_freq, as 54% of the nominal frequency:
253 253
254 54% of 2933 MHz = 1583 MHz 254 54% of 2933 MHz = 1583 MHz
255 255
256 Nominal frequency is the maximum frequency of 256 Nominal frequency is the maximum frequency of the processor, and it usually
257 corresponds to the frequency of the P0 P-stat 257 corresponds to the frequency of the P0 P-state.
258 258
259 2.4 related_cpus: 259 2.4 related_cpus:
260 ----------------- 260 -----------------
261 The related_cpus field is identical to affect 261 The related_cpus field is identical to affected_cpus.
262 262
263 affected_cpus : 4 263 affected_cpus : 4
264 related_cpus : 4 264 related_cpus : 4
265 265
266 Currently, the PCC driver does not evaluate _ 266 Currently, the PCC driver does not evaluate _PSD. The platforms that support
267 PCC do not implement SW_ALL. So OSPM doesn't 267 PCC do not implement SW_ALL. So OSPM doesn't need to perform any coordination
268 to ensure that the same frequency is requeste 268 to ensure that the same frequency is requested of all dependent CPUs.
269 269
270 3. Caveats: 270 3. Caveats:
271 ----------- 271 -----------
272 The "cpufreq_stats" module in its present for 272 The "cpufreq_stats" module in its present form cannot be loaded and
273 expected to work with the PCC driver. Since t 273 expected to work with the PCC driver. Since the "cpufreq_stats" module
274 provides information wrt each P-state, it is 274 provides information wrt each P-state, it is not applicable to the PCC driver.
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