16.2. Software execution models in big.LITTLE

There are two primary execution models for big.LITTLE:

Migration

Migration models are a natural extension to power-performance management techniques such as DVFS, (see Dynamic voltage and frequency scaling).

The migration model has two types:

  • Cluster migration.

  • CPU migration.

A migration action is similar to a DVFS operating point transition. Operating points on the DVFS curve of a core are traversed in response to load variations. When the current core (or cluster) has attained the highest operating point, if the software stack requires more performance, a core (or cluster) migration action is effected. Execution then continues on the other core (or cluster) with the operating points on this core (or cluster) being traversed. When performance is not required, execution can switch back.

Global Task Scheduling

In Global Task Scheduling (see Global Task Scheduling), the operating system task scheduler is aware of the differences in compute capacity between big and LITTLE cores. The scheduler tracks the performance requirement for each individual software thread, and uses that information to decide which type of core to use for each. Unused cores can be powered off. This approach has a number of advantages over the migration models.

Copyright © 2015 ARM. All rights reserved.ARM DEN0024A
Non-ConfidentialID050815