[Question] How to fix the order in which commands run?

[MikeBusuttil]

I'm working on a repo where running scons results in 12 commands being run. For optimal performance, many commands can be run in parallel (see "Optimal Order of Commands" below). I believe our scons configuration results in sub-optimal command running. Would anyone be able to help me figure out what the current command ordering is now and how to tell scons to parallelize the offending commands?

Scons configuration files

• Sconstruct
• Sconscipt
• opendbc/dbc/Sconscipt
• opendbc/can/Sconscipt
• site_scons/site_tools/cython.py

Optimal Order of Commands

graph LR;
    A[g++ -o common.os];
    B[g++ -o dbc.os];
    C[g++ -o parser.os];
    D[g++ -o packer.os];
    E[g++ -o libdbc.so];
    F[cythonize packer_pyx.pyx];
    G[g++ -o packer_pyx.o];
    H[g++ -o packer_pyx.so];
    I[cythonize parser_pyx.pyx];
    J[g++ -o parser_pyx.o];
    K[g++ -o parser_pyx.so];
    L[python3 generator.py];
    A-->E;
    B-->E;
    B-->H;
    B-->K;
    C-->E;
    D-->E;
    F-->G;
    G-->H;
    I-->J;
    J-->K;
    Start-->A;
    Start-->B;
    Start-->C;
    Start-->D;
    Start-->F;
    Start-->I;
    Start-->L;

Loading

Commands resulting from scons

1. g++ -o opendbc/can/common.os -c -std=c++1z -DDBC_FILE_PATH='"/root/opendbc/opendbc/dbc"' -g -fPIC -O0 -Wunused -Werror -Wshadow -Wno-vla-cxx-extension -Wno-unknown-warning-option -fPIC -I. -I/usr/lib/include -I/opt/homebrew/include -I/usr/include/python3.12 opendbc/can/common.cc
2. g++ -o opendbc/can/dbc.os -c -std=c++1z -DDBC_FILE_PATH='"/root/opendbc/opendbc/dbc"' -g -fPIC -O0 -Wunused -Werror -Wshadow -Wno-vla-cxx-extension -Wno-unknown-warning-option -fPIC -I. -I/usr/lib/include -I/opt/homebrew/include -I/usr/include/python3.12 opendbc/can/dbc.cc
3. g++ -o opendbc/can/parser.os -c -std=c++1z -DDBC_FILE_PATH='"/root/opendbc/opendbc/dbc"' -g -fPIC -O0 -Wunused -Werror -Wshadow -Wno-vla-cxx-extension -Wno-unknown-warning-option -fPIC -I. -I/usr/lib/include -I/opt/homebrew/include -I/usr/include/python3.12 opendbc/can/parser.cc
4. g++ -o opendbc/can/packer.os -c -std=c++1z -DDBC_FILE_PATH='"/root/opendbc/opendbc/dbc"' -g -fPIC -O0 -Wunused -Werror -Wshadow -Wno-vla-cxx-extension -Wno-unknown-warning-option -fPIC -I. -I/usr/lib/include -I/opt/homebrew/include -I/usr/include/python3.12 opendbc/can/packer.cc
5. cythonize opendbc/can/packer_pyx.pyx
6. cythonize opendbc/can/parser_pyx.pyx
7. python3 opendbc/dbc/generator/generator.py
8. g++ -o opendbc/can/packer_pyx.o -c -std=c++1z -g -fPIC -O0 -Wunused -Wshadow -Wno-vla-cxx-extension -Wno-unknown-warning-option -Wno-#warnings -Wno-shadow -Wno-deprecated-declarations -I. -I/usr/lib/include -I/opt/homebrew/include -I/usr/include/python3.12 -I.venv/lib/python3.12/site-packages/numpy/_core/include opendbc/can/packer_pyx.cpp
9. g++ -o opendbc/can/parser_pyx.o -c -std=c++1z -g -fPIC -O0 -Wunused -Wshadow -Wno-vla-cxx-extension -Wno-unknown-warning-option -Wno-#warnings -Wno-shadow -Wno-deprecated-declarations -I. -I/usr/lib/include -I/opt/homebrew/include -I/usr/include/python3.12 -I.venv/lib/python3.12/site-packages/numpy/_core/include opendbc/can/parser_pyx.cpp
10. g++ -o opendbc/can/libdbc.so -shared opendbc/can/dbc.os opendbc/can/parser.os opendbc/can/packer.os opendbc/can/common.os -Lopendbc/can -L/opt/homebrew/lib
11. g++ -o opendbc/can/packer_pyx.so -pthread -shared -Wl,-rpath=/root/opendbc/opendbc/can opendbc/can/packer_pyx.o -Lopendbc/can -L/opt/homebrew/lib -Lopendbc/can -ldbc
12. g++ -o opendbc/can/parser_pyx.so -pthread -shared -Wl,-rpath=/root/opendbc/opendbc/can opendbc/can/parser_pyx.o -Lopendbc/can -L/opt/homebrew/lib -Lopendbc/can -ldbc -lre2

Why I believe the command order is sub-optimal

• scons -j16 takes 3.25s to run
• the following node script (which hard-codes the run order) takes 2.4s to run

const util = require('util');
const exec = util.promisify(require('child_process').exec);

chains = [
  [
    [
      `g++ -o opendbc/can/common.os -c -std=c++1z -DDBC_FILE_PATH='"/root/opendbc/opendbc/dbc"' -g -fPIC -O0 -Wunused -Werror -Wshadow -Wno-vla-cxx-extension -Wno-unknown-warning-option -fPIC -I. -I/usr/lib/include -I/opt/homebrew/include -I/usr/include/python3.12 opendbc/can/common.cc`,
      `g++ -o opendbc/can/dbc.os -c -std=c++1z -DDBC_FILE_PATH='"/root/opendbc/opendbc/dbc"' -g -fPIC -O0 -Wunused -Werror -Wshadow -Wno-vla-cxx-extension -Wno-unknown-warning-option -fPIC -I. -I/usr/lib/include -I/opt/homebrew/include -I/usr/include/python3.12 opendbc/can/dbc.cc`,
      `g++ -o opendbc/can/parser.os -c -std=c++1z -DDBC_FILE_PATH='"/root/opendbc/opendbc/dbc"' -g -fPIC -O0 -Wunused -Werror -Wshadow -Wno-vla-cxx-extension -Wno-unknown-warning-option -fPIC -I. -I/usr/lib/include -I/opt/homebrew/include -I/usr/include/python3.12 opendbc/can/parser.cc`,
      `g++ -o opendbc/can/packer.os -c -std=c++1z -DDBC_FILE_PATH='"/root/opendbc/opendbc/dbc"' -g -fPIC -O0 -Wunused -Werror -Wshadow -Wno-vla-cxx-extension -Wno-unknown-warning-option -fPIC -I. -I/usr/lib/include -I/opt/homebrew/include -I/usr/include/python3.12 opendbc/can/packer.cc`,
    ],
    [
      `g++ -o opendbc/can/libdbc.so -shared opendbc/can/dbc.os opendbc/can/parser.os opendbc/can/packer.os opendbc/can/common.os -Lopendbc/can -L/opt/homebrew/lib`,
    ],
  ],
  [
    [`cythonize opendbc/can/packer_pyx.pyx`],
    [`g++ -o opendbc/can/packer_pyx.o -c -std=c++1z -g -fPIC -O0 -Wunused -Wshadow -Wno-vla-cxx-extension -Wno-unknown-warning-option -Wno-#warnings -Wno-shadow -Wno-deprecated-declarations -I. -I/usr/lib/include -I/opt/homebrew/include -I/usr/include/python3.12 -I.venv/lib/python3.12/site-packages/numpy/_core/include opendbc/can/packer_pyx.cpp`],
    [`g++ -o opendbc/can/packer_pyx.so -pthread -shared -Wl,-rpath=/root/opendbc/opendbc/can opendbc/can/packer_pyx.o -Lopendbc/can -L/opt/homebrew/lib -Lopendbc/can -ldbc`], // race condition: this must be run after "g++ -o opendbc/can/dbc.os" completes
  ],
  [
    [`cythonize opendbc/can/parser_pyx.pyx`],
    [`g++ -o opendbc/can/parser_pyx.o -c -std=c++1z -g -fPIC -O0 -Wunused -Wshadow -Wno-vla-cxx-extension -Wno-unknown-warning-option -Wno-#warnings -Wno-shadow -Wno-deprecated-declarations -I. -I/usr/lib/include -I/opt/homebrew/include -I/usr/include/python3.12 -I.venv/lib/python3.12/site-packages/numpy/_core/include opendbc/can/parser_pyx.cpp`],
    [`g++ -o opendbc/can/parser_pyx.so -pthread -shared -Wl,-rpath=/root/opendbc/opendbc/can opendbc/can/parser_pyx.o -Lopendbc/can -L/opt/homebrew/lib -Lopendbc/can -ldbc -lre2`], // race condition: this must be run after "g++ -o opendbc/can/dbc.os" completes
  ],
  [
    [`python3 opendbc/dbc/generator/generator.py`],
  ],
]

const run_series = async(chain) => {
  for(cmds of chain) {
    await Promise.all(cmds.map(cmd => exec(cmd)))
  }
}

for(const chain of chains) {
  run_series(chain)
}

[bdbaddog]

Have you tried using scons --tree=all to see all the dependencies which SCons is aware of?
What's the command line you're using to run SCons which results in the build log you've shared above?
How many cores does your machine have?

[MikeBusuttil]

Have you tried using scons --tree=all to see all the dependencies which SCons is aware of?

ya, I get a tree with 2090 lines (generated files) but no indication of the 12 commands that generated those files

What's the command line you're using to run SCons which results in the build log you've shared above?

scons -j$(nproc)

How many cores does your machine have?

16 cores

Thanks for responding so fast @bdbaddog 🚀!!

[MikeBusuttil]

After further investigation I now believe that scons actually does run the commands in the optimal order. I now believe the time difference is because of scons overhead. The scons: Reading SConscript files ... step appears to take ~1s to run which fully accounts for the difference.