Lines Matching refs:the
11 * it under the terms of the GNU General Public License as published by
12 * the Free Software Foundation; version 2 of the License.
14 * This program is distributed in the hope that it will be useful, but
15 * WITHOUT ANY WARRANTY; without even the implied warranty of
17 * INFRINGEMENT. See the GNU General Public License for more details.
19 * You should have received a copy of the GNU General Public License along
20 * with this program; if not, write to the Free Software Foundation, Inc.,
46 Processor Clocking Control (PCC) is an interface between the platform
48 performance (ie: frequency) between the platform firmware and the OS.
50 The PCC driver (pcc-cpufreq) allows OSPM to take advantage of the PCC
53 OS utilizes the PCC interface to inform platform firmware what frequency the
55 the requested frequency. If the request for the target frequency could not be
65 between the OS and platform firmware. PCC also implements a "doorbell" that
66 is used by the OS to inform the platform firmware that a command has been
69 The ACPI PCCH() method is used to discover the location of the PCC shared
70 memory region. The shared memory region header contains the "command" and
71 "status" interface. PCCH() also contains details on how to access the platform
74 The following commands are supported by the PCC interface:
79 used to discover the offsets for the input and output buffers in the shared
82 When PCC mode is enabled, the platform will not expose processor performance
84 the native P-state driver (such as acpi-cpufreq for Intel, powernow-k8 for
88 computes the required performance for each processor based on server workload.
89 The PCC driver fills in the command interface, and the input buffer and
90 communicates the request to the platform firmware. The platform firmware is
91 responsible for delivering the requested performance.
93 Each PCC command is "global" in scope and can affect all the logical CPUs in
94 the system. Therefore, PCC is capable of performing "group" updates. With PCC
95 the OS is capable of getting/setting the frequency of all the logical CPUs in
96 the system with a single call to the BIOS.
100 This command is used by the OSPM to query the running frequency of the
101 processor since the last time this command was completed. The output buffer
102 indicates the average unhalted frequency of the logical processor expressed as
103 a percentage of the nominal (ie: maximum) CPU frequency. The output buffer
104 also signifies if the CPU frequency is limited by a power budget condition.
108 This command is used by the OSPM to communicate to the platform firmware the
111 OSPM if the desired frequency was achieved or not.
115 The PCC driver will load on any system where the platform firmware:
116 * supports the PCC interface, and the associated PCCH() and PCCP() methods
117 * assumes responsibility for managing the hardware clocking controls in order
118 to deliver the requested processor performance
120 Currently, certain HP ProLiant platforms implement the PCC interface. On those
121 platforms PCC is the "default" choice.
124 such an instance, as is also the case on platforms where the PCC interface
125 is not implemented, the PCC driver will fail to load silently.
129 When the driver loads, it merely prints the lowest and the highest CPU
130 frequencies supported by the platform firmware.
136 This means that the OPSM can request the CPU to run at any frequency in
137 between the limits (1600 MHz, and 2933 MHz) specified in the message.
139 Internally, there is no need for the driver to convert the "target" frequency
142 The VERSION number for the driver will be of the format v.xy.ab.
146 | -- this will increase with bug fixes/enhancements to the driver
147 |-- this is the version of the PCC specification the driver adheres to
150 The following is a brief discussion on some of the fields exported via the
151 /sys filesystem and how their values are affected by the PCC driver:
156 frequencies need to be listed because the BIOS will try to achieve any
157 frequency, within limits, requested by the governor. A frequency does not have
168 in the scaling_available_frequencies or scaling_cur_freq, or scaling_max_freq.
170 conditions are met the BIOS can achieve a slightly higher speed than requested
176 B) There is a round-off error associated with the cpuinfo_cur_freq value.
177 Since the driver obtains the current frequency as a "percentage" (%) of the
178 nominal frequency from the BIOS, sometimes, the values displayed by
184 In this example, the nominal frequency is 2933 MHz. The driver obtains the
185 current frequency, cpuinfo_cur_freq, as 54% of the nominal frequency:
189 Nominal frequency is the maximum frequency of the processor, and it usually
190 corresponds to the frequency of the P0 P-state.
199 Currently, the PCC driver does not evaluate _PSD. The platforms that support
201 to ensure that the same frequency is requested of all dependent CPUs.
206 expected to work with the PCC driver. Since the "cpufreq_stats" module
207 provides information wrt each P-state, it is not applicable to the PCC driver.