1.. BSD LICENSE 2 Copyright(c) 2010-2014 Intel Corporation. All rights reserved. 3 All rights reserved. 4 5 Redistribution and use in source and binary forms, with or without 6 modification, are permitted provided that the following conditions 7 are met: 8 9 * Redistributions of source code must retain the above copyright 10 notice, this list of conditions and the following disclaimer. 11 * Redistributions in binary form must reproduce the above copyright 12 notice, this list of conditions and the following disclaimer in 13 the documentation and/or other materials provided with the 14 distribution. 15 * Neither the name of Intel Corporation nor the names of its 16 contributors may be used to endorse or promote products derived 17 from this software without specific prior written permission. 18 19 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 20 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 21 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 22 A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 23 OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 24 SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 25 LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 28 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 29 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30 31Power Management 32================ 33 34The DPDK Power Management feature allows users space applications to save power 35by dynamically adjusting CPU frequency or entering into different C-States. 36 37* Adjusting the CPU frequency dynamically according to the utilization of RX queue. 38 39* Entering into different deeper C-States according to the adaptive algorithms to speculate 40 brief periods of time suspending the application if no packets are received. 41 42The interfaces for adjusting the operating CPU frequency are in the power management library. 43C-State control is implemented in applications according to the different use cases. 44 45CPU Frequency Scaling 46--------------------- 47 48The Linux kernel provides a cpufreq module for CPU frequency scaling for each lcore. 49For example, for cpuX, /sys/devices/system/cpu/cpuX/cpufreq/ has the following sys files for frequency scaling: 50 51* affected_cpus 52 53* bios_limit 54 55* cpuinfo_cur_freq 56 57* cpuinfo_max_freq 58 59* cpuinfo_min_freq 60 61* cpuinfo_transition_latency 62 63* related_cpus 64 65* scaling_available_frequencies 66 67* scaling_available_governors 68 69* scaling_cur_freq 70 71* scaling_driver 72 73* scaling_governor 74 75* scaling_max_freq 76 77* scaling_min_freq 78 79* scaling_setspeed 80 81In the DPDK, scaling_governor is configured in user space. 82Then, a user space application can prompt the kernel by writing scaling_setspeed to adjust the CPU frequency 83according to the strategies defined by the user space application. 84 85Core-load Throttling through C-States 86------------------------------------- 87 88Core state can be altered by speculative sleeps whenever the specified lcore has nothing to do. 89In the DPDK, if no packet is received after polling, 90speculative sleeps can be triggered according the strategies defined by the user space application. 91 92Per-core Turbo Boost 93-------------------- 94 95Individual cores can be allowed to enter a Turbo Boost state on a per-core 96basis. This is achieved by enabling Turbo Boost Technology in the BIOS, then 97looping through the relevant cores and enabling/disabling Turbo Boost on each 98core. 99 100API Overview of the Power Library 101--------------------------------- 102 103The main methods exported by power library are for CPU frequency scaling and include the following: 104 105* **Freq up**: Prompt the kernel to scale up the frequency of the specific lcore. 106 107* **Freq down**: Prompt the kernel to scale down the frequency of the specific lcore. 108 109* **Freq max**: Prompt the kernel to scale up the frequency of the specific lcore to the maximum. 110 111* **Freq min**: Prompt the kernel to scale down the frequency of the specific lcore to the minimum. 112 113* **Get available freqs**: Read the available frequencies of the specific lcore from the sys file. 114 115* **Freq get**: Get the current frequency of the specific lcore. 116 117* **Freq set**: Prompt the kernel to set the frequency for the specific lcore. 118 119* **Enable turbo**: Prompt the kernel to enable Turbo Boost for the specific lcore. 120 121* **Disable turbo**: Prompt the kernel to disable Turbo Boost for the specific lcore. 122 123User Cases 124---------- 125 126The power management mechanism is used to save power when performing L3 forwarding. 127 128References 129---------- 130 131* l3fwd-power: The sample application in DPDK that performs L3 forwarding with power management. 132 133* The "L3 Forwarding with Power Management Sample Application" chapter in the *DPDK Sample Application's User Guide*. 134