Skip to content

bricks/_common/Makefile: Enable CSUPEROPT for smaller binaries. #402

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom
Merged
merged 1 commit into from
Nov 3, 2025
Merged

bricks/_common/Makefile: Enable CSUPEROPT for smaller binaries. #402

merged 1 commit into from
Nov 3, 2025

Conversation

@laurensvalk
Copy link
Member

@laurensvalk laurensvalk commented Oct 14, 2025 •
edited
Loading

Looks like we were missing considerable savings with this build option.

Reduces build size:

  • Move Hub: -2400
  • Technic Hub: -2332

Looks like MicroPython enables this for:

ifeq ($(MCU_SERIES),$(filter $(MCU_SERIES),f0 g0 l0))
CSUPEROPT = -Os # save some code space

For everything else:

# some code is performance bottleneck and compiled with other optimization options
CSUPEROPT = -O3

Which is probably to optimize for speed. We also find in the MicroPython source:

# Force nlr code to always be compiled with space-saving optimisation so
# that the function preludes are of a minimal and predictable form.
$(PY_BUILD)/nlr%.o: CFLAGS += -Os

# optimising gc for speed; 5ms down to 4ms on pybv2
$(PY_BUILD)/gc.o: CFLAGS += $(CSUPEROPT)

# optimising vm for speed, adds only a small amount to code size but makes a huge difference to speed (20% faster)
$(PY_BUILD)/vm.o: CFLAGS += $(CSUPEROPT)
# Optimizing vm.o for modern deeply pipelined CPUs with branch predictors
# may require disabling tail jump optimization. This will make sure that
# each opcode has its own dispatching jump which will improve branch
# branch predictor efficiency.
# https://marc.info/?l=lua-l&m=129778596120851
# http://hg.python.org/cpython/file/b127046831e2/Python/ceval.c#l828
# http://www.emulators.com/docs/nx25_nostradamus.htm
#-fno-crossjumping

@laurensvalk
Copy link
Member Author

laurensvalk commented Oct 14, 2025 •
edited
Loading

So maybe we should follow and only apply it to F0 (City Hub and Move Hub)? Although Technic Hub is closer to the space limit than City Hub, so could be worth doing that if we don't mind the speed penalty. I.e. perhaps do it on Move Hub only.

@github-actions
Copy link

github-actions bot commented Oct 14, 2025 •
edited
Loading

Download the artifacts for this pull request:

@coveralls
Copy link

coveralls commented Oct 14, 2025 •
edited
Loading

Coverage Status

coverage: 57.143%. remained the same
when pulling 0b854ba on CSUPEROPT
into 3fe9ffc on master.

@laurensvalk laurensvalk requested a review from dlech October 14, 2025 11:53
@dlech
Copy link
Member

dlech commented Oct 14, 2025

Apparently that comment has a different idea about what small code size is. 😮

Sounds reasonable to use -Os for this on hubs that are getting close to full.

@laurensvalk
Copy link
Member Author

laurensvalk commented Oct 14, 2025 •
edited
Loading

Apparently that comment has a different idea about what small code size is. 😮

20% speed increase for 0.5% build size (2K on 400K builds) is probably worth it for most boards where space is not an issue. We can make the trade-off the other way.

Sounds reasonable to use -Os for this on hubs that are getting close to full.

👍

I came across this option as I was working on a new embedded simulation build (which had it enabled by default), so even if this is all to come out of that, it was worth it 😄

@laurensvalk
bricks/technichub,movehub: Set CSUPEROPT for build size.
0b854ba 
Reduces build size:
Move Hub: -2400
Technic Hub: -2400

At the cost of slightly slower performance of the VM.

These hubs are almost running out of space, so this
is more important.
@laurensvalk
Copy link
Member Author

laurensvalk commented Nov 3, 2025

On Technic Hub, the savings are 2400 bytes at a reduction of only 635 to 611 pystones/sec, so -4%, which is certainly worth it.

@laurensvalk laurensvalk merged commit 0b854ba into master Nov 3, 2025
31 checks passed
@laurensvalk
Copy link
Member Author

laurensvalk commented Nov 3, 2025 •
edited
Loading

The savings are even larger, but we are also seeing that there was a big initial bump in size on going to MicroPython 1.26.

image

For Move Hub, there wasn't a jump when going to 1.26:

image

So it might have been a specific feature rather than the base becoming much larger. And maybe this feature isn't needed on Technic Hub either. Part of this is floating point support, but this covers only a portion of the increase (about 350 bytes).

@dlech dlech deleted the CSUPEROPT branch November 3, 2025 13:45
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Reviewers

@dlech dlech Awaiting requested review from dlech

Assignees

No one assigned

Labels

None yet

Projects

None yet

Milestone

No milestone

Development

Successfully merging this pull request may close these issues.

4 participants

@laurensvalk @coveralls @dlech