Upgrade from Zephyr 3.4 to 3.5 causes performance issues on SAMx7x

[mcscholtz]

I recently moved our project from Zephyr 3.4 to 3.5 and noticed that the CPU usage has gone from spending about 60-63% in idle to about ~24-28%. This is after changing some of the most active threads to kernel threads instead of user threads. Without doing that it is so slow I cannot even see the console printing anything out.

This is a problem because it affects response times. The platform for the application is atmel SAME70 (Cortex M7). I looked here and did some kernel diffs. However there does not appear to be any major changes to this platform. I ensured the clock speed was configured to be the same and that the cache was still enabled.

The same application runs well on Zephyr 3.4, perhaps there was some change I am unaware of?

The only major change I noticed in the generated Kconfig file was that libc was changed to Picolibc, which does not seem to be the source of the problem.

Any thoughts? Thanks