Raspberry Pi OS 32-bit vs. 64-bit Performance
phoronix.com
phoronix.com
In fact, hypothetically assuming the same instruction set, 64-bit can cause performance degradation over 32-bit, particularly in memory-bound benchmarks, because the size of memory pointers and default int size will take up twice as much space, which puts stress on the limited cache space, which will generate additional off chip memory accesses.
'int' size stays the same. 'long' gets bigger (on LP64 platforms).
Apart from that, I would agree with your assessment.
I'm sorry when I was in university there were still SPARC64 machines around, which use the "ILP64" where the default int size increased to 64 bits, so that must have been why I was taught that the default int size increased when going to 64-bit arch.
Possible; IIRC, we had the same thing on x86 because the jump to AMD64 meant that you could depend on certain extensions (SSE2?) that didn't exist on all previous processors but which were present on all 64-bit processors. So it became a split where code compiled for 64-bit CPUs knew it could depend on those extensions without even needing a runtime check, which was nice. That said, my understanding is that for data-heavy workloads it really does help to move twice as much data per operation.
Anybody know how software support is looking for 64Bit? OS support is good but presumably the software itself needs to be arm 64 compiled too?
I've said this before, that instead of focusing on building a custom distro everyone would benefit if they instead focused on just enabling all the other distro's and OS's. Pretty much everything, including windows runs on the darn thing, its the closest piece of HW in the arm ecosystem (other than the server class machines) to a random PC motherboard when it comes to just about working with any given OS.
That said, yes one would very much hope that everyone can work together to make the diff between Debian and its downstreams as small as possible given the constraints that each party operates under.
I've used both the original Raspbian 64-bit builds and plain Debian 64-bit with the few required RaspberryPi specific tools added in. Kernels are all self-built (cross-compiled) keeping up with mainline Linux.
That's quite impressive!
> As a rule of thumb you need almost twice as much RAM with a 64-bit userland compared to 32-bit with the same programs/services running. [1]
[1]: https://github.com/ThomasKaiser/sbc-bench/blob/master/Result...
That doesn't make sense; going 64-bit should only double the size of pointers, it shouldn't touch the size of code or data in memory.