image size slightly increased from NCS 2.9.2 to NCS 3.1.0 - any option/config switches to reduce it?

[Achim Kraus]

Building the sample "nrf/samples/cellular/udp" with "west build -b nrf9160dk/nrf9160/ns" using

NCS 2.9.2 results in:

Memory region         Used Size  Region Size  %age Used
           FLASH:       81852 B       992 KB      8.06%
             RAM:       16072 B     211608 B      7.60%
        IDT_LIST:          0 GB        32 KB      0.00%

with NCS 3.1.0 in:

Memory region         Used Size  Region Size  %age Used
           FLASH:       83988 B       992 KB      8.27%
             RAM:       17992 B     211608 B      8.50%
        IDT_LIST:          0 GB        32 KB      0.00%

while it may be just "as it is", I'm wondering, if that's the result of different compiler options or different project configs (even when my own "prj.conf" is pretty much the same). 

[Hieu]

Hi Achim,

For general size optimization techniques, you can refer to these guides:
Memory footprint optimization
sdk-zephyr/samples/basic/minimal at ncs-v3.1.0 · nrfconnect/sdk-zephyr
Optimizing for Footprint

There are also a few tweaks you can do with C Library selection. The Minimal sample linked above use CONFIG_MINIMAL_LIBC. If you need features that it doesn't support, you can also use CONFIG_PICOLIBC, enable CONFIG_PICOLIBC_USE_MODULE to build it from source, and CONFIG_PICOLIBC_SIZE_OPTIMIZATIONS to optimize for size.

A tip not usually mentioned is use reduced cbprintf support with CONFIG_CBPRINTF_NANO.

Another such tip is using Link Time Optimization with CONFIG_LTO.

As for possible increase from changes in the sample, I will have to research further and follow-up in a few workdays.

Hieu

[Hieu]

Hi Achim,

The only change directly to the sample is:
https://github.com/nrfconnect/sdk-nrf/commit/97438ec100ee074b3b96b8350dc7713bf76c69f3.

It is not something that can be reverted, however, due to other change in the SDK. You can find details in the commit.

Hieu

[Achim Kraus]

Thanks for the general hints. I used the sample to demonstrate the increase in size. But I observe that also for other (own/non-Nordic) apps (in some cases up to 10k more). Therefore I was asking myself, if there is something general changed by intention, e.g. compiler flags or similar things.

[Hieu]

According to release notes, the only thing that can match here seems to be a general kernel performance improvement. Please refer to: Zephyr 4.1.0 Release Note.

[Achim Kraus]

Thanks, I guess the slightly increase must just be accepted.