Re: Raspberry Pi 3B energy consumption

[clement.aldebert@univ-tlse3.fr]

Dear Alex Bennée,

Thank you for your response and for the provided documentation link.

To clarify, when we refer to energy consumption, we are specifically looking at CPU core utilization. Our goal is to ensure that when we turn off CPU cores on the emulated Raspberry Pi 3B, the host machine does not keep its corresponding cores running at 100% utilization.

This is particularly relevant for our use case, as our supervisor, M. Poquet, intends to use this project for teaching operating system development. Students using QEMU to emulate a Raspberry Pi 3B may have different host machines, so our objective is to implement a general approach that ensures CPU core deactivation works properly regardless of the host system.

So far, our measurements indicate that even after turning off cores in the emulated system, all CPU cores on the host remain at 100% utilization. We are exploring ways to improve this behavior.

We have looked into using -icount, but we would like to find a more viable solution, particularly for the Cortex-A53 CPU used in the Raspberry Pi 3B. Ideally, we would like to be able to use -smp 1 without being constrained by QEMU’s limitations and to implement proper CPU core shutdown, similar to what is available on x86-64 architectures.

Would you have any recommendations or insights on achieving better power management in this scenario?

Best regards,
Clément Aldebert & Laurent Polzin

----- Mail original -----
De: "Alex Bennée" <alex.bennee@linaro.org>
À: "Polzini" <laurentpolzin@gmail.com>
Cc: qemu-devel@nongnu.org, qemu-arm@nongnu.org, "millian poquet" <millian.poquet@univ-tlse3.fr>, "clement aldebert" <clement.aldebert@univ-tlse3.fr>
Envoyé: Mercredi 19 Mars 2025 16:57:41
Objet: Re: Raspberry Pi 3B energy consumption

Polzini <laurentpolzin@gmail.com> writes:

> Dear Sir/Madam, My name is Clément Aldebert, and I am a third-year computer science student at Paul Sabatier University.
> Together with my teammate Laurent Polzin, we are working on a project supervised by Millian Poquet. Our project focuses on
> reducing the energy consumption of QEMU’s Raspberry Pi 3B emulation, as we have observed that power usage is quite high
> even when the system is idle.

Can you qualify that a bit more? What are you running the emulation on?
What power usage do you see?

Power consumption of the emulation is really just down to computational
efficiency of the emulation and if we ever get to a point that QEMU can
go idle giving the host system a chance to reach a lower power state.

> Ultimately, we also aim to enable emulation on a single CPU core.

If you want to run all emulation on a single core you could use -icount
to do that. It is less efficient though.

> We are reaching out to
> inquire if you have any advice, resources, or suggestions for implementing power management in QEMU, particularly for the
> Raspberry Pi 3B model. Additionally, we would like to understand any constraints or best practices regarding adding new
> code or features to QEMU.

What documentation that exists can be found in the developers section of
the manual:

  https://qemu.readthedocs.io/en/master/devel/index.html

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro