[TF-M] FF PSA API overhead

Hi,

the performance improvement presentation[0] reports a FF PSA API overhead of 20 000 CPU cycles for the psa_call. Which is 300 us for a 64MHz CPU.

This is quite a lot of instructions and I am concerned about whether real world embedded application's will have time to call these secure services.

I'm interested in isolation level 2.

I understand that it is not possible to have isolation level 2 with library mode. But what about SFN mode, could that eventually support isolation level 2?

If not, what is the current status of optimizing the service call overhead for IPC.

Is it considered to be as optimized as it can be or is there still hope for optimizing further?

[0] https://www.trustedfirmware.org/docs/tf-m_forum_20211209-TF-M_Performance-Im...