`--parallel` improvements (#13800)

* improve make parallel jobs support

* document the --parallel option

* disable the output-sync for interactive targets

4 files changed, 25 insertions, 8 deletions

diff --git a/lib/python/qmk/cli/compile.py b/lib/python/qmk/cli/compile.py
index 7a45e7721..acbd77864 100755
--- a/lib/python/qmk/cli/compile.py
+++ b/lib/python/qmk/cli/compile.py
@@ -18,7 +18,7 @@ from qmk.keymap import keymap_completer
 @cli.argument('-kb', '--keyboard', type=keyboard_folder, completer=keyboard_completer, help='The keyboard to build a firmware for. Ignored when a configurator export is supplied.')
 @cli.argument('-km', '--keymap', completer=keymap_completer, help='The keymap to build a firmware for. Ignored when a configurator export is supplied.')
 @cli.argument('-n', '--dry-run', arg_only=True, action='store_true', help="Don't actually build, just show the make command to be run.")
-@cli.argument('-j', '--parallel', type=int, default=1, help="Set the number of parallel make jobs to run.")
+@cli.argument('-j', '--parallel', type=int, default=1, help="Set the number of parallel make jobs; 0 means unlimited.")
 @cli.argument('-e', '--env', arg_only=True, action='append', default=[], help="Set a variable to be passed to make. May be passed multiple times.")
 @cli.argument('-c', '--clean', arg_only=True, action='store_true', help="Remove object files before compiling.")
 @cli.subcommand('Compile a QMK Firmware.')
diff --git a/lib/python/qmk/cli/flash.py b/lib/python/qmk/cli/flash.py
index 1b2932a5b..c2d9e09c6 100644
--- a/lib/python/qmk/cli/flash.py
+++ b/lib/python/qmk/cli/flash.py
@@ -38,7 +38,7 @@ def print_bootloader_help():
 @cli.argument('-km', '--keymap', help='The keymap to build a firmware for. Use this if you dont have a configurator file. Ignored when a configurator file is supplied.')
 @cli.argument('-kb', '--keyboard', type=keyboard_folder, completer=keyboard_completer, help='The keyboard to build a firmware for. Use this if you dont have a configurator file. Ignored when a configurator file is supplied.')
 @cli.argument('-n', '--dry-run', arg_only=True, action='store_true', help="Don't actually build, just show the make command to be run.")
-@cli.argument('-j', '--parallel', type=int, default=1, help="Set the number of parallel make jobs to run.")
+@cli.argument('-j', '--parallel', type=int, default=1, help="Set the number of parallel make jobs; 0 means unlimited.")
 @cli.argument('-e', '--env', arg_only=True, action='append', default=[], help="Set a variable to be passed to make. May be passed multiple times.")
 @cli.argument('-c', '--clean', arg_only=True, action='store_true', help="Remove object files before compiling.")
 @cli.subcommand('QMK Flash.')
diff --git a/lib/python/qmk/cli/multibuild.py b/lib/python/qmk/cli/multibuild.py
index bdb0b493c..85ed0fa1e 100755
--- a/lib/python/qmk/cli/multibuild.py
+++ b/lib/python/qmk/cli/multibuild.py
@@ -10,7 +10,7 @@ from subprocess import DEVNULL
 from milc import cli
 
 from qmk.constants import QMK_FIRMWARE
-from qmk.commands import _find_make
+from qmk.commands import _find_make, get_make_parallel_args
 import qmk.keyboard
 import qmk.keymap
 
@@ -28,7 +28,7 @@ def _is_split(keyboard_name):
     return True if 'SPLIT_KEYBOARD' in rules_mk and rules_mk['SPLIT_KEYBOARD'].lower() == 'yes' else False
 
 
-@cli.argument('-j', '--parallel', type=int, default=1, help="Set the number of parallel make jobs to run.")
+@cli.argument('-j', '--parallel', type=int, default=1, help="Set the number of parallel make jobs; 0 means unlimited.")
 @cli.argument('-c', '--clean', arg_only=True, action='store_true', help="Remove object files before compiling.")
 @cli.argument('-f', '--filter', arg_only=True, action='append', default=[], help="Filter the list of keyboards based on the supplied value in rules.mk. Supported format is 'SPLIT_KEYBOARD=yes'. May be passed multiple times.")
 @cli.argument('-km', '--keymap', type=str, default='default', help="The keymap name to build. Default is 'default'.")
@@ -80,7 +80,7 @@ all: {keyboard_safe}_binary
                 )
                 # yapf: enable
 
-    cli.run([make_cmd, '-j', str(cli.args.parallel), '-f', makefile.as_posix(), 'all'], capture_output=False, stdin=DEVNULL)
+    cli.run([make_cmd, *get_make_parallel_args(cli.args.parallel), '-f', makefile.as_posix(), 'all'], capture_output=False, stdin=DEVNULL)
 
     # Check for failures
     failures = [f for f in builddir.glob(f'failed.log.{os.getpid()}.*')]
diff --git a/lib/python/qmk/commands.py b/lib/python/qmk/commands.py
index 8c66228b2..421453d83 100644
--- a/lib/python/qmk/commands.py
+++ b/lib/python/qmk/commands.py
@@ -52,7 +52,7 @@ def create_make_target(target, parallel=1, **env_vars):
     for key, value in env_vars.items():
         env.append(f'{key}={value}')
 
-    return [make_cmd, '-j', str(parallel), *env, target]
+    return [make_cmd, *get_make_parallel_args(parallel), *env, target]
 
 
 def create_make_command(keyboard, keymap, target=None, parallel=1, **env_vars):
@@ -112,6 +112,24 @@ def get_git_version(current_time, repo_dir='.', check_dir='.'):
     return current_time
 
 
+def get_make_parallel_args(parallel=1):
+    """Returns the arguments for running the specified number of parallel jobs.
+    """
+    parallel_args = []
+
+    if int(parallel) <= 0:
+        # 0 or -1 means -j without argument (unlimited jobs)
+        parallel_args.append('--jobs')
+    else:
+        parallel_args.append('--jobs=' + str(parallel))
+
+    if int(parallel) != 1:
+        # If more than 1 job is used, synchronize parallel output by target
+        parallel_args.append('--output-sync=target')
+
+    return parallel_args
+
+
 def create_version_h(skip_git=False, skip_all=False):
     """Generate version.h contents
     """
@@ -185,8 +203,7 @@ def compile_configurator_json(user_keymap, bootloader=None, parallel=1, **env_va
         make_command.append('-s')
 
     make_command.extend([
-        '-j',
-        str(parallel),
+        *get_make_parallel_args(parallel),
         '-r',
         '-R',
         '-f',