ceph/src/dpdk/doc/guides/prog_guide/power_man.rst

   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
  31 Power Management
  32 ================
  33
  34 The DPDK Power Management feature allows users space applications to save power
  35 by 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
  42 The interfaces for adjusting the operating CPU frequency are in the power management library.
  43 C-State control is implemented in applications according to the different use cases.
  44
  45 CPU Frequency Scaling
  46 ---------------------
  47
  48 The Linux kernel provides a cpufreq module for CPU frequency scaling for each lcore.
  49 For 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
  81 In the DPDK, scaling_governor is configured in user space.
  82 Then, a user space application can prompt the kernel by writing scaling_setspeed to adjust the CPU frequency
  83 according to the strategies defined by the user space application.
  84
  85 Core-load Throttling through C-States
  86 -------------------------------------
  87
  88 Core state can be altered by speculative sleeps whenever the specified lcore has nothing to do.
  89 In the DPDK, if no packet is received after polling,
  90 speculative sleeps can be triggered according the strategies defined by the user space application.
  91
  92 API Overview of the Power Library
  93 ---------------------------------
  94
  95 The main methods exported by power library are for CPU frequency scaling and include the following:
  96
  97 *   **Freq up**: Prompt the kernel to scale up the frequency of the specific lcore.
  98
  99 *   **Freq down**: Prompt the kernel to scale down the frequency of the specific lcore.
 100
 101 *   **Freq max**: Prompt the kernel to scale up the frequency of the specific lcore to the maximum.
 102
 103 *   **Freq min**: Prompt the kernel to scale down the frequency of the specific lcore to the minimum.
 104
 105 *   **Get available freqs**: Read the available frequencies of the specific lcore from the sys file.
 106
 107 *   **Freq get**: Get the current frequency of the specific lcore.
 108
 109 *   **Freq set**: Prompt the kernel to set the frequency for the specific lcore.
 110
 111 User Cases
 112 ----------
 113
 114 The power management mechanism is used to save power when performing L3 forwarding.
 115
 116 References
 117 ----------
 118
 119 *   l3fwd-power: The sample application in DPDK that performs L3 forwarding with power management.
 120
 121 *   The "L3 Forwarding with Power Management Sample Application" chapter in the *DPDK Sample Application's User Guide*.