CFLAGS Rpi3B Rpi3B+ Rpi4

[antonellocaroli]

Hi,

I use for these three boards always

CFLAGS="-march=native -O2 -pipe"

Is it okay or better to use anything else? If so, which ones?

[NeddySeagoon]

antonellocaroli,

The answer depends if you use 32 bit or 64 bit.

In 64 bit mode on the Pi3B and 3B+ I use

[antonellocaroli]

Thank you, Neddy,

now if I change the cflags, should I recompile the entire system including the gcc?

Yes, I use a 64bit system.

[NeddySeagoon]

NeddySeagoon,

On the Pi3, No. I suspect nothing changes, since in order execution is probably the default.

On the Pi4, probably not. The speed gains will be marginal.
The instructions will not change, only the order in which they are issued. Keep an eye on 64 Bit Raspberry Pi 4B Benchmarks
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

[antonellocaroli]

Hi NeddySeagoon,

but on 32-bit systems what do you use as cflags?
for both rpi3 and rpi4?

[roylongbottom]

I found that, after experimenting with alternatives, that just -O3 was best, for a particular set of calculation. See details here:

https://forums-web2.gentoo.org/viewtopic-p-8364700.html?sid=32d336b7f2b4f2b7f4c0d77c97eeeeef#8364700

This was when compiling on a Pi 4.
_________________
Regards

Roy

[antonellocaroli]

if I compile on Rpi4 with these cflags

CFLAGS="-mcpu=cortex-a53+crc -mtune=cortex-a53 -ftree-vectorize -O2 -pipe -fomit-frame-pointer"

or

CFLAGS="-mcpu=cortex-a53+crc -mtune=cortex-a53 -ftree-vectorize -O3 -pipe -fomit-frame-pointer"

Can I use the same stage on rpi3?

always referring to 32 bits...

[roylongbottom]

In attempting to run at maximum speeds with multithreading, for 32 bit floating point programs up to gcc 8, I use:

[antonellocaroli]

my question comes from the fact that the rpi4 is more performing in the compilation of the 3.

I generally produce

a system for:
rpi3 32 bit
rpi3 64 bit
rpi4 32bit
rpi4 64 bit

I would like to produce the stage4 related to the 4 systems all on the rpi4 (if possible?)
changing the cflags in make.conf

for rpi4 64 bit use
CFLAGS="-mcpu=cortex-a53+crc -mtune=cortex-a72 -ftree-vectorize -O2 -pipe -fomit-frame-pointer"

could I know precisely the 4 cflags in make.conf how they should be?
I am not an expert in this field.

[roylongbottom]

As you can see, I just use simple gcc commands from Terminal, easy to change for trying different options, but they are for short self contained programs.

I should have quoted 64 bit gcc 9 results. These are from the same 64 bit compilation, running on 4B, 3B+ and 3B