Turbo Frequency and Power Consumption

I use a PicoPSU-like solution with a 120W external adapter. Sometimes the i5-9400F PC consumes up to 96W. I feel uncomfortable about it and decide to lower power consumption by setting a new turbo frequency limit.

Monitor CPU Frequency

To monitor CPU frequency and refresh every 1 second:

$watch -n 1 "cat /proc/cpuinfo | grep MHz"

Every 10.0s: cat /proc/cpuinfo | grep MHz     i5-9400F: Sat Jul  9 20:51:25 2022

cpu MHz         : 900.000
cpu MHz         : 1095.972
cpu MHz         : 800.000
cpu MHz         : 800.000
cpu MHz         : 800.000
cpu MHz         : 800.000

To increase the update interval to every 2 seconds, change ‘1’ to ‘2’. To decrease to 0.1 seconds, change ‘1’ to ‘.1’.

Customize Turbo Boost Frequency

In Gigabyte H310M S2V 2.0’s BIOS menu, open the [MIT] tab ➞ [Advanced Frequency Settings] ➞ [Advanced CPU Core Settings] page. Assign new integer values in the Turbo Ratio options.

To decrease the upper limit for 400MHz on i5-9400F, update the “Auto” field as below:

Turbo Ratio (1-Core Active)	37	41
Turbo Ratio (2-Core Active)	36	40
Turbo Ratio (3-Core Active)	36	40
Turbo Ratio (4-Core Active)	36	40
Turbo Ratio (5-Core Active)	35	39
Turbo Ratio (6-Core Active)	35	39

Customize Turbo Ratio

The [Advanced CPU Core Settings] page in BIOS.

Better Power Control

i5-9400F	Turbo On (Default up to 4.1GHz)	Turbo On (Customize up to 3.7GHz)	Turbo Off (Base 2.9GHz)
Max Power consumption	96W	77W	60W

Turbo settings and the max power conmption.

Decreasing the upper limit for 400MHz helps to manage the max power consumption within 77W. While the CPU runs 600MHz to 800MHz faster than the base 2.9GHz, it is still 19W lower than the default Turbo settings. I think this is a good balance. There is no need to disable Turbo Boost to save power in this case.

For notebooks, Joel found that “Disabling Intel Turbo Boost Has a Huge Impact on Battery Life”. It is because that “…Clearly, turning on Turbo Boost exacts a power consumption penalty…” and “…power consumption increases significantly under load when you augment clock rate and voltage…”.

Also, “…Turbo Boost is most effective at improving the performance of poorly-threaded applications…”. If it cannot accelerate programs with acceptable power usage, consider lowering the turbo limit or disabling it.

Reference

1. LinuxHint: How Do I Find CPU Frequency in Linux?
2. Software Engineering Authority: How to get CPU Frequency in Linux
3. die.net: watch(1) – Linux man page
4. Tom’s Hardware: Experiment: Does Intel’s Turbo Boost Trump Overclocking? Page 10: Power Consumption
5. Tom’s Hardware: Experiment: Does Intel’s Turbo Boost Trump Overclocking? Page 11: Conclusion
6. HardwareTimes: Intel 11th Gen Rocket Lake-S CPU Power Consumption Explained
7. ExtremeTech: Disabling Intel Turbo Boost Has a Huge Impact on Battery Life