Measuring Workload Power

These elements facilitate collecting the power data that can be used to determine the required cooling capacity to maintain temperatures within a target range for the application's workload:

  • Active heatsink properly attached to the module
  • BIOS settings configured for maximum system performance
  • Stable and robust platform power supply that exceeds the workload needs
  • All accessory devices connected and operational for the defined use case

Use the following instructions to configure the platform, collect the data, and calculate the ideal power limit settings and minimum cooling capacity required.

Configure BIOS to allow maximum module performance

  1. In the CPU settings > System Power Options menu, enable Intel® Turbo Boost Technology and configure Power Limit options as shown:

  1. Use the Go Back option to reach the Thermal Configuration Parameters menu.

  2. Set the Thermal Control Offset to 0, disable Automatic Thermal Reporting, and set Critical and Passive trip points to 103 C, as shown:

  1. Use the Go Back option and press F4 to commit changes to BIOS.

Theory of measuring processor power

Processor power will be measured by accessing the RAPL driver’s energy counter and recording periodic results to a log file for later analysis. The energy counter counts the amount of energy spent by the processor in micro (1x10-6) joules. Therefore, processor power can be calculated by logging two instances of the energy counter and then dividing the difference by the measurement interval.

RAPL driver’s energy counter can be accessed at /sys/class/powercap/intel-rapl/intel-rapl:0/energy_uj.

Using a shell script to capture power data

  1. Stop executing Thermal Daemon to halt operating system based thermal controls.

  1. Power measurement script example to collect power, in watts, every two seconds (adjust as appropriate).

  1. Run your application and the power measurement script simultaneously to collect workload data.

Reading the log to determine peak power consumption

After running the target application through all use cases and long enough to collect sufficient data, stop the logging script activity and open the log file. The long file contains Watts used expressed as integers.

Module power limit (PL1) should be set at the next whole number above maximum power recorded.

Heatsink selection for example application

This chart shows the ambient temperature (Y-axis) range for a known workload (application power PL1) when using either the passive reference heatsink or the reference heatsink for a forced air fan.

Our example 2.5 Watt application can run with the reference heatsink as long as the ambient temperature remains below 30 ˚C.

With the reference heatsink and forced air fan solution, a 7 Watt application could run in an ambient environment of up to 25 ˚C.

Configure BIOS settings for characterized results

  1. In the CPU settings > System Power Options menu, verify that Intel® Turbo Boost Technology is enabled, and set Power Limit 1 to the next whole number aboce the maximum power recorded in the log file. It is 3 for our 2.5 watt application example.

  1. Use the Go Back option and press F4 to commit changes to BIOS.
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