Linux Plumbers Conference 2024

Session

Power Management and Thermal Control MC

19 Sept 2024, 10:00

Matrix chat

Description

The Power Management and Thermal Control microconference is about all things related to saving energy and managing heat. Among other things, we care about thermal control infrastructure, CPU and device power-management mechanisms, energy models, and power capping. In particular, we are interested in improving and extending thermal control support in the Linux kernel and utilizing energy-saving features of modern hardware.

The general goal is to facilitate cross-framework and cross-platform discussions that can help improve energy-awareness and thermal control in Linux.

Since the previous iteration of this microconference, several topics covered by it have been addressed, including:

• Writable trip points support:

https://lore.kernel.org/linux-pm/6017196.lOV4Wx5bFT@kreacher/

• Limiting thermal netlink messaging to the cases when there are subscribers:

https://lore.kernel.org/linux-pm/20240223155942.60813-1-stanislaw.gruszka@linux.intel.com/

• Support for runtime-modifiable Energy Models:

https://lore.kernel.org/linux-pm/20240117095714.1524808-1-lukasz.luba@arm.com/

• Thermal control diagnostics and debug support:

https://lore.kernel.org/linux-pm/20240109094112.2871346-1-daniel.lezcano@linaro.org/
https://lore.kernel.org/linux-pm/20240109094112.2871346-2-daniel.lezcano@linaro.org/

and there is work in progress related to some of them:

• Temperature sensor aggregation support:

https://lore.kernel.org/linux-pm/20240119110842.772606-1-abailon@baylibre.com/

• Virtualized CPU performance scaling:

https://lore.kernel.org/linux-pm/20240127004321.1902477-1-davidai@google.com/

This year we will mostly talk about thermal control subsystem enhancements, including user trip points and PID thermal governor, thermal and performance control interfaces for devices, system suspend support enhancements and power/energy estimation tooling.

Presentation materials

Live stream

250. Enhancements and adjustments of the thermal control subsystem

Rafael Wysocki (Intel Open Source Technology Center)

19/09/2024, 10:10

For the last year the thermal control subsystem in the Linux kernel has been undergoing an extensive redesign resulting in some code simplifications, enhancements and fixes for known issues. However, there are still ways to improve it. Among other things, the following changes may be considered:

• Introduction of a thermal core testing facility.
• Finalizing the elimination of trip point...

86. Userspace trip points

Daniel Lezcano (Linaro)

19/09/2024, 10:30

The trip points are used by the kernel to start mitigating a specific thermal zone when a temperature crosses this limit. This action is taken to protect the silicon. The userspace thermal management has a more complex logic where it takes into account multiple sources of information like the temperatures, the usage and the current application profile to sustain the performance. It readjusts...

87. PID / timer based governor

Daniel Lezcano (Linaro)

19/09/2024, 10:50

The step wise governor is largely used by all mobile platforms. Those are more and more performant, so overheating very quickly. Given the speed of the temperature transitions, the step wise governor does not have enough time to apply the right cooling effect as it must go through several iteration to reach the temperature drop. Several iterations means hundreds of milliseconds. During this...

85. Power / Thermal / Performance interfaces

Daniel Lezcano (Linaro)

19/09/2024, 11:10

The userspace which has a complex logic to manage the thermal envelope of the platform is often platform specific because custom kernels export clumsily interfaces to act on PM. Therefore, the userspace is often unusable when we want to support mainline kernels. That leads to more work as there are multiple userspace implementation to achieve the same goal. The objective of the discussion /...

185. Wattson: trace based power/energy estimation

Samuel Wu, Saravana Kannan

19/09/2024, 12:00

As a community, we pay a lot of attention to the performance impact of the changes we land. Especially when it comes to areas like scheduler/cpufreq that are expected to have a significant impact on performance. This is possible because we have good benchmarks to quickly iterate over and check the impact of our patches.

However when it comes to checking the power/energy impact of our...

260. Optimizing suspend/resume

Saravana Kannan

19/09/2024, 12:20

Optimizing suspend/resume time makes a significant difference for UX
and power savings. Especially for wearable devices which typically
have small CPUs and small batteries. This talk will point out all the
gaps we've found so far and what we could do to address them and some
of my TODOs to get there.

• Optimizing global async suspend/resume
• Using runtime PM to avoid resume/suspend...

298. Supporting suspend-to-idle for legacy platforms

Ulf Hansson (Linaro)

19/09/2024, 12:40

On legacy platforms it's common to support suspend-to-ram (S2R), but not suspend-to-idle (S2I). In many cases, this seems to be because of some limitations in the FW that deals with CPU power-management.

For various reasons, we want to promote S2I in favor of S2R due to the benefit it provides, but it's not always possible to convince vendors to update their FW for legacy platforms.

In a...

235. Supporting multiple low power modes for system wide suspend

Dhruva Gole

In the TI K3 AM62 Family of devices the hardware supports multiple Low Power Modes that retain context in the DRAM. However, Linux doesn't have direct awareness or any solid framework that allows a user to select a particular system-wide low power mode. This makes it challenging for any user to select which low power mode to enter in the SoC.
After discussions with the community and with...