power_man.rst revision 97f17497
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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
92API Overview of the Power Library
93---------------------------------
94
95The 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
111User Cases
112----------
113
114The power management mechanism is used to save power when performing L3 forwarding.
115
116References
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*.
122