FileSystem Backend Log Overwrite takes a lot of CPU

[sguitton01]

Hi all,

I am working on an nrf5340 and I activated the FileSystem Backend log to save the logs in my external Flash.
It's working how we are expecting to except once the flash is full. Once the system starts to overwrite data, we see a huge increase of CPU usage. At this point the logging thread is switching for from 5% of the CPU usage to 80%.. 
Were you aware of this behaviour? Is there some way to optimize this?

Thank you,

Sylvain

[Sigurd Hellesvik]

Hi,

Once the system starts to overwrite data, we see a huge increase of CPU usage.

Erasing flash is a time-consuming procedure, and the CPU has to pause during this operations. I am not fully sure how this works with erasing external flash, but it may be similar.
Here is the file and place where the driver erases the flash:
https://github.com/nrfconnect/sdk-zephyr/blob/c989b977d31eddf4b90eaf2f146740b6f4c8109a/drivers/flash/nrf_qspi_nor.c#L582

Can you add some logging to this function? Then you can see how often and how large areas are erased. That might give us some insight into this.

Regards,
Sigurd Hellesvik