Why do the maximum frequencies of TX2 CPUs drop to 1.4GHz when more than 4 cores are up?

Robotics & Edge Computing Jetson & Embedded Systems Jetson TX2
1

Hello,

The TX2 SOM datasheet says:
“CPU Maximum Operating Frequency: 1-4 core = up to 2.0GHz; greater than 4-core = up to 1.4GHz”

Can you please tell us the reason why the max freq drops to 1.4GHz when more than 6 cores are up?

When I put all 6 cores online, the following Linux command shows all 6 cores are still at 2GHz. Is the reading from Linux reliable?

cat /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq

2021000
2034000
2036000
2017000
2024000
2026000

Thanks for your help!

2

Is the frequency drop due to the limited power supply to CPU subsystem?

3

Have you set a particular power model? “sudo nvpmodel -m 0” makes the maximum performance range available. If you want to force to max performance within a given model, then run “sudo jetson_clocks” after switching to the desired model (for older releases it is “sudo ~ubuntu/jetson_clocks.sh”).

4

The power consumption would drive the temperature of the die beyond its maximum operating point, so it is necessary to throttle the freq lower.

5

Thank you, Trumany!

6

Hi, Trumany,

I have some follow-up questions for this topic.
If we have a very strong CPU fan on top of SOM and keep the CPU cores cool, can the CPU cores still keep 2GHz frequency? Will the HW or nVIDIA bootloader limit the max freq to 1.4GHz even if the temperature of CPU core is low?

Thanks
Yan

7

Yes, it is limited for most use case.

8

Hi, Trumany,

Thank you for confirming the throttling of the max freq is enforced by the design regardless of the CPU temperature! What still confuses me is the output of CPU frequencies by Linux.
When I put all 6 cores online and run CPU intensive stress testing (CPU scaling_governor is set to performance mode), the following Linux command shows all 6 cores are still at 2GHz either during the testing or after the testing. Is the reading from this Linux command reliable? Is there any other Linux command (such as reading other sysfs node) which can show accurate CPU frequencies of cores on TX2?

cat /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq

2021000
2034000
2036000
2017000
2024000
2026000

Thank you!