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SPDX-License-Identifier: BSD-3-Clause 2 Copyright(c) 2010-2014 Intel Corporation. 3 4Power Management 5================ 6 7The DPDK Power Management feature allows users space applications to save power 8by dynamically adjusting CPU frequency or entering into different C-States. 9 10* Adjusting the CPU frequency dynamically according to the utilization of RX queue. 11 12* Entering into different deeper C-States according to the adaptive algorithms to speculate 13 brief periods of time suspending the application if no packets are received. 14 15The interfaces for adjusting the operating CPU frequency are in the power management library. 16C-State control is implemented in applications according to the different use cases. 17 18CPU Frequency Scaling 19--------------------- 20 21The Linux kernel provides a cpufreq module for CPU frequency scaling for each lcore. 22For example, for cpuX, /sys/devices/system/cpu/cpuX/cpufreq/ has the following sys files for frequency scaling: 23 24* affected_cpus 25 26* bios_limit 27 28* cpuinfo_cur_freq 29 30* cpuinfo_max_freq 31 32* cpuinfo_min_freq 33 34* cpuinfo_transition_latency 35 36* related_cpus 37 38* scaling_available_frequencies 39 40* scaling_available_governors 41 42* scaling_cur_freq 43 44* scaling_driver 45 46* scaling_governor 47 48* scaling_max_freq 49 50* scaling_min_freq 51 52* scaling_setspeed 53 54In the DPDK, scaling_governor is configured in user space. 55Then, a user space application can prompt the kernel by writing scaling_setspeed to adjust the CPU frequency 56according to the strategies defined by the user space application. 57 58Core-load Throttling through C-States 59------------------------------------- 60 61Core state can be altered by speculative sleeps whenever the specified lcore has nothing to do. 62In the DPDK, if no packet is received after polling, 63speculative sleeps can be triggered according the strategies defined by the user space application. 64 65Per-core Turbo Boost 66-------------------- 67 68Individual cores can be allowed to enter a Turbo Boost state on a per-core 69basis. This is achieved by enabling Turbo Boost Technology in the BIOS, then 70looping through the relevant cores and enabling/disabling Turbo Boost on each 71core. 72 73Use of Power Library in a Hyper-Threaded Environment 74---------------------------------------------------- 75 76In the case where the power library is in use on a system with Hyper-Threading enabled, 77the frequency on the physical core is set to the highest frequency of the Hyper-Thread siblings. 78So even though an application may request a scale down, the core frequency will 79remain at the highest frequency until all Hyper-Threads on that core request a scale down. 80 81API Overview of the Power Library 82--------------------------------- 83 84The main methods exported by power library are for CPU frequency scaling and include the following: 85 86* **Freq up**: Prompt the kernel to scale up the frequency of the specific lcore. 87 88* **Freq down**: Prompt the kernel to scale down the frequency of the specific lcore. 89 90* **Freq max**: Prompt the kernel to scale up the frequency of the specific lcore to the maximum. 91 92* **Freq min**: Prompt the kernel to scale down the frequency of the specific lcore to the minimum. 93 94* **Get available freqs**: Read the available frequencies of the specific lcore from the sys file. 95 96* **Freq get**: Get the current frequency of the specific lcore. 97 98* **Freq set**: Prompt the kernel to set the frequency for the specific lcore. 99 100* **Enable turbo**: Prompt the kernel to enable Turbo Boost for the specific lcore. 101 102* **Disable turbo**: Prompt the kernel to disable Turbo Boost for the specific lcore. 103 104User Cases 105---------- 106 107The power management mechanism is used to save power when performing L3 forwarding. 108 109 110Empty Poll API 111-------------- 112 113Abstract 114~~~~~~~~ 115 116For packet processing workloads such as DPDK polling is continuous. 117This means CPU cores always show 100% busy independent of how much work 118those cores are doing. It is critical to accurately determine how busy 119a core is hugely important for the following reasons: 120 121 * No indication of overload conditions 122 * User does not know how much real load is on a system, resulting 123 in wasted energy as no power management is utilized 124 125Compared to the original l3fwd-power design, instead of going to sleep 126after detecting an empty poll, the new mechanism just lowers the core frequency. 127As a result, the application does not stop polling the device, which leads 128to improved handling of bursts of traffic. 129 130When the system become busy, the empty poll mechanism can also increase the core 131frequency (including turbo) to do best effort for intensive traffic. This gives 132us more flexible and balanced traffic awareness over the standard l3fwd-power 133application. 134 135 136Proposed Solution 137~~~~~~~~~~~~~~~~~ 138The proposed solution focuses on how many times empty polls are executed. 139The less the number of empty polls, means current core is busy with processing 140workload, therefore, the higher frequency is needed. The high empty poll number 141indicates the current core not doing any real work therefore, we can lower the 142frequency to safe power. 143 144In the current implementation, each core has 1 empty-poll counter which assume 1451 core is dedicated to 1 queue. This will need to be expanded in the future to 146support multiple queues per core. 147 148Power state definition: 149^^^^^^^^^^^^^^^^^^^^^^^ 150 151* LOW: Not currently used, reserved for future use. 152 153* MED: the frequency is used to process modest traffic workload. 154 155* HIGH: the frequency is used to process busy traffic workload. 156 157There are two phases to establish the power management system: 158^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 159* Training phase. This phase is used to measure the optimal frequency 160 change thresholds for a given system. The thresholds will differ from 161 system to system due to differences in processor micro-architecture, 162 cache and device configurations. 163 In this phase, the user must ensure that no traffic can enter the 164 system so that counts can be measured for empty polls at low, medium 165 and high frequencies. Each frequency is measured for two seconds. 166 Once the training phase is complete, the threshold numbers are 167 displayed, and normal mode resumes, and traffic can be allowed into 168 the system. These threshold number can be used on the command line 169 when starting the application in normal mode to avoid re-training 170 every time. 171 172* Normal phase. Every 10ms the run-time counters are compared 173 to the supplied threshold values, and the decision will be made 174 whether to move to a different power state (by adjusting the 175 frequency). 176 177API Overview for Empty Poll Power Management 178~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 179* **State Init**: initialize the power management system. 180 181* **State Free**: free the resource hold by power management system. 182 183* **Update Empty Poll Counter**: update the empty poll counter. 184 185* **Update Valid Poll Counter**: update the valid poll counter. 186 187* **Set the Frequency Index**: update the power state/frequency mapping. 188 189* **Detect empty poll state change**: empty poll state change detection algorithm then take action. 190 191User Cases 192---------- 193The mechanism can applied to any device which is based on polling. e.g. NIC, FPGA. 194 195References 196---------- 197 198* The :doc:`../sample_app_ug/l3_forward_power_man` 199 chapter in the :doc:`../sample_app_ug/index` section. 200 201* The :doc:`../sample_app_ug/vm_power_management` 202 chapter in the :doc:`../sample_app_ug/index` section. 203