Experimenting with 64bit Raspbian OS on netPI

[Armin@netPI]

I continued experimenting with 64Bit compared to 32Bit.

I heard rumors that using 64Bit might cause higher memory consumption in terms of FLASH and RAM memory. But what is true in reality?

Following the ARM whitepaper here https://community.arm.com/developer/ip-p...arm-64-bit I learned that the ARM64 instruction set is always 32bit in lengths. So it is not like 64bit mode would double the code size.

But for data a value of the fundamental type "long" for example is now 64Bits wide, while a "long" under 32bit condition was 32bit. Types "char" and "short" remain at 8 respectively 16bits. So it is expected that code containing a lot of constants of type "long" will need for more space for code.

And indeed, the two containers arm32v7/debian and arm64v8/debian differ in their sizes. Here is what I got when I compared the image sizes under docker

Code:

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
arm64v8/debian      buster-20191014     b59066e92117        5 weeks ago         108MB
...
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
arm32v7/debian      buster-20191014     f67434cf7768        5 weeks ago         92.8MB

You see the 64bit image is about 16% larger.

But how about the RAM memory consumption ... I had two SD cards with the 32Bit and 64Bit setup running during my tests. I know just looking to plain containerized Debian doesn't count much since it is not a real application but at least it might show a trend.

So I used a console connecting to the containers and called the command "free" to look for the used overall memory including the OS itself and the container:

32Bit:

Code:

             total        used        free      shared  buff/cache   available
Mem:         948304      144676      112180        1052      691448      754180
Swap:        102396        8192       94204

64Bit:

Code:

             total        used        free      shared  buff/cache   available
Mem:         939024      145136      477276        6460      316612      733800
Swap:        102396           0      102396

If you now compare the "used" values you see there is not much difference the higher memory consumption of a 64Bit compilation is negligible.

To be continued ...