On 3/19/2020 7:59 AM, David McMackins wrote:
It's worth noting that Raspbian is still only distributed in 32-bit
form, failing to take full advantage of the 64-bit ARM processor on the
Pi 4. If some other distribution is built for arm64, that may well
perform better than Raspbian even though it is the best "supported" OS.
The 32-bit distribution was a conscious decision by the Raspberry Pi
Foundation to maintain binary compatibility with older Pi boards so that
newcomers would not be confused about which download to choose.
I don't know how much of an effect running in 32-bit mode has on the
performance of the newer CPU, but I thought it was worth mentioning as a
possible reason why an unofficial distribution might run better on a Pi 4.
I doubt that there is any noticeable difference, given that the biggest
model (RAM wise) is just 4GB. And it is a myth for most practical cases
that 64bit code is automatically faster (or better) than 32bit code.
Beside an additional problem that any unofficial 64bit ARM distros are
facing is properly supporting the 32bit GPU, which can cause rather a
penalty then any serious improvement in performance.
Just recompiling C code for 64bit target rather than 32bit just doesn't
make things go faster automagically (that applies not only to ARM, but
x86/64 processors as well). A /long/ will still be a /long/ and hence
32bit, which might on 64bit wide CPU registers need additional
instructions to deal with the superfluous 32bits in the register. Only
dealing for doubles (A LOT!) might make a substantial difference, if the
compiler library is written that way. And newer instructions to move
memory usually are only of advantage when working in a +4GB
environment. What ever gain you make in a 4GB environment might simply
be lost by dealing with additional overhead with the default data types,
and you can bet that there only a handful if any applications in Linux
land that have been rewritten to use different data types on different
CPU architectures...
Ralf
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