LVC20-110 Skin temperature management with hierarchical constraints

Session Abstract

Due to the increasing complexity of SoCs, we're now seeing lots of thermal sensors on the die to quickly detect hot spots and allow the OS to take steps to mitigate these events. The Linux thermal framework provides mechanisms such as inputs for better scheduling, frequency throttling, idle injection and turning on fans to prevent the silicon from getting damaged from overheating. This is also called as junction temperature management.

The Linux thermal framework is also used for managing the skin temperature of a device - the temperature that users feel when they hold and use the device. However, this skin temperature management involves manual characterization of performance states for devices such as CPU and GPU to its effect on the skin temperature of the device.

So the framework is doing two distinct tasks: preventing silicon damage and preventing skin burns for users by capping the power of a device. We feel these tasks should be handled by different frameworks.

We're currently experimenting with the kernel's energy model to dynamically build a hierarchy of power constraints and allow the platform integrator to set limits for each power domain using the powercap framework. This will allow the kernel to manage the power consumption (and hence dissipation) budget of the various devices on the Soc more autonomously, leading to better performance at a given power budget instead of overcoming the primary goal of the thermal framework which is mitigate at the limits.

Attendees are expected to know a little bit about how the current thermal framework works but don't need to know all the technical details. We will cover the conceptual differences between the current and proposed models as an introduction in the talk.

Session Speakers

Daniel Lezcano

Linaro - Senior Engineer - Power specialist (Linaro)

Daniel worked in 1998 in the Space Industry and Air traffic management for distributed system project in life safety constraints. He acquired for this project a system programming expertise. <br /> <br /> He joined IBM in 2004 and since this date he does kernel hacking and pushed upstream the resource virtualization with the namespaces. He is the author and maintainer of the Linux Container (LXC).<br /> <br /> In 2012, he joined Linaro to work in the power management team. Deeply involved in the power management improvements for the different members of Linaro, he continues to contribute and maintain some parts of the Linux kernel.

Amit Kucheria

Sr. Engineer, Qualcomm Landing Team (Linaro)

Amit works at Linaro and has been found dabbling in the upstream Linux community in the areas of power and thermal management. He was once found lost in the friendly Zephyr RTOS community for a bit.<br><br>In the last decade, he’s led the Power Management working group at Linaro, helped lead the effort to bring powerful developer boards at low-cost to the software community and helped several SoC vendors to work with the upstream community and help themselves along the way.<br><br>His main hobby these days is to learn to grow food.

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