[dpdk-dev] [PATCH v7 3/4] doc/guides/proguides/power-man: update the power API

Liang Ma liang.j.ma at intel.com
Tue Sep 4 16:10:27 CEST 2018


update the document for empty poll API.

Signed-off-by: Liang Ma <liang.j.ma at intel.com>
---
 doc/guides/prog_guide/power_man.rst | 87 +++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)

diff --git a/doc/guides/prog_guide/power_man.rst b/doc/guides/prog_guide/power_man.rst
index eba1cc6..d8a4ef7 100644
--- a/doc/guides/prog_guide/power_man.rst
+++ b/doc/guides/prog_guide/power_man.rst
@@ -106,6 +106,93 @@ 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 do not know how much real load is on a system meaning
+          resulted 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:
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+* Initialization/Training phase. The training phase is necessary
+  in order to figure out the system polling baseline numbers from
+  idle to busy. The highest poll count will be during idle, where all
+  polls are empty. These poll counts will be different between
+  systems due to the many possible processor micro-arch, cache
+  and device configurations, hence the training phase.
+  In the training phase, traffic is blocked so the training algorithm
+  can average the empty-poll numbers for the LOW, MED and
+  HIGH  power states in order to create a baseline.
+  The core's counter are collected every 10ms, and the Training
+  phase will take 2 seconds.
+
+* Normal phase. When the training phase is complete, traffic is
+  started. The run-time poll counts are compared with the
+  baseline and the decision will be taken to move to MED power
+  state or HIGH power state. The counters are calculated every
+  10ms.
+
+
+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 Fequence Index**: update the power state/frequency mapping.
+
+* **Detect empty poll state change**: empty poll state change detection algorithm.
+
+User Cases
+----------
+The mechanism can applied to any device which is based on polling. e.g. NIC, FPGA.
+
 References
 ----------
 
-- 
2.7.5



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