-.. BSD LICENSE
- Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
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- from this software without specific prior written permission.
-
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- OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.. SPDX-License-Identifier: BSD-3-Clause
+ Copyright(c) 2010-2014 Intel Corporation.
Power Management
================
-The Intel® DPDK Power Management feature allows users space applications to save power
+The DPDK Power Management feature allows users space applications to save power
by dynamically adjusting CPU frequency or entering into different C-States.
* Adjusting the CPU frequency dynamically according to the utilization of RX queue.
* scaling_setspeed
-In the Intel® DPDK, scaling_governor is configured in user space.
+In the DPDK, scaling_governor is configured in user space.
Then, a user space application can prompt the kernel by writing scaling_setspeed to adjust the CPU frequency
according to the strategies defined by the user space application.
-------------------------------------
Core state can be altered by speculative sleeps whenever the specified lcore has nothing to do.
-In the Intel® DPDK, if no packet is received after polling,
+In the DPDK, if no packet is received after polling,
speculative sleeps can be triggered according the strategies defined by the user space application.
+Per-core Turbo Boost
+--------------------
+
+Individual cores can be allowed to enter a Turbo Boost state on a per-core
+basis. This is achieved by enabling Turbo Boost Technology in the BIOS, then
+looping through the relevant cores and enabling/disabling Turbo Boost on each
+core.
+
+Use of Power Library in a Hyper-Threaded Environment
+----------------------------------------------------
+
+In the case where the power library is in use on a system with Hyper-Threading enabled,
+the frequency on the physical core is set to the highest frequency of the Hyper-Thread siblings.
+So even though an application may request a scale down, the core frequency will
+remain at the highest frequency until all Hyper-Threads on that core request a scale down.
+
API Overview of the Power Library
---------------------------------
* **Freq set**: Prompt the kernel to set the frequency for the specific lcore.
+* **Enable turbo**: Prompt the kernel to enable Turbo Boost for the specific lcore.
+
+* **Disable turbo**: Prompt the kernel to disable Turbo Boost for the specific lcore.
+
User Cases
----------
The power management mechanism is used to save power when performing L3 forwarding.
+
+Empty Poll API
+--------------
+
+Abstract
+~~~~~~~~
+
+For packet processing workloads such as DPDK polling is continuous.
+This means CPU cores always show 100% busy independent of how much work
+those cores are doing. It is critical to accurately determine how busy
+a core is hugely important for the following reasons:
+
+ * No indication of overload conditions
+ * User does not know how much real load is on a system, resulting
+ in wasted energy as no power management is utilized
+
+Compared to the original l3fwd-power design, instead of going to sleep
+after detecting an empty poll, the new mechanism just lowers the core frequency.
+As a result, the application does not stop polling the device, which leads
+to improved handling of bursts of traffic.
+
+When the system become busy, the empty poll mechanism can also increase the core
+frequency (including turbo) to do best effort for intensive traffic. This gives
+us more flexible and balanced traffic awareness over the standard l3fwd-power
+application.
+
+
+Proposed Solution
+~~~~~~~~~~~~~~~~~
+The proposed solution focuses on how many times empty polls are executed.
+The less the number of empty polls, means current core is busy with processing
+workload, therefore, the higher frequency is needed. The high empty poll number
+indicates the current core not doing any real work therefore, we can lower the
+frequency to safe power.
+
+In the current implementation, each core has 1 empty-poll counter which assume
+1 core is dedicated to 1 queue. This will need to be expanded in the future to
+support multiple queues per core.
+
+Power state definition:
+^^^^^^^^^^^^^^^^^^^^^^^
+
+* LOW: Not currently used, reserved for future use.
+
+* MED: the frequency is used to process modest traffic workload.
+
+* HIGH: the frequency is used to process busy traffic workload.
+
+There are two phases to establish the power management system:
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+* Training phase. This phase is used to measure the optimal frequency
+ change thresholds for a given system. The thresholds will differ from
+ system to system due to differences in processor micro-architecture,
+ cache and device configurations.
+ In this phase, the user must ensure that no traffic can enter the
+ system so that counts can be measured for empty polls at low, medium
+ and high frequencies. Each frequency is measured for two seconds.
+ Once the training phase is complete, the threshold numbers are
+ displayed, and normal mode resumes, and traffic can be allowed into
+ the system. These threshold number can be used on the command line
+ when starting the application in normal mode to avoid re-training
+ every time.
+
+* Normal phase. Every 10ms the run-time counters are compared
+ to the supplied threshold values, and the decision will be made
+ whether to move to a different power state (by adjusting the
+ frequency).
+
+API Overview for Empty Poll Power Management
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+* **State Init**: initialize the power management system.
+
+* **State Free**: free the resource hold by power management system.
+
+* **Update Empty Poll Counter**: update the empty poll counter.
+
+* **Update Valid Poll Counter**: update the valid poll counter.
+
+* **Set the Frequency Index**: update the power state/frequency mapping.
+
+* **Detect empty poll state change**: empty poll state change detection algorithm then take action.
+
+User Cases
+----------
+The mechanism can applied to any device which is based on polling. e.g. NIC, FPGA.
+
References
----------
-* l3fwd-power: The sample application in Intel® DPDK that performs L3 forwarding with power management.
+* The :doc:`../sample_app_ug/l3_forward_power_man`
+ chapter in the :doc:`../sample_app_ug/index` section.
-* The "L3 Forwarding with Power Management Sample Application" chapter in the *Intel® DPDK Sample Application's User Guide*.
+* The :doc:`../sample_app_ug/vm_power_management`
+ chapter in the :doc:`../sample_app_ug/index` section.
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