support/tests: allow top-level parallel builds

Running tests with top-level parallel builds can speed up running some
tests, expecially those that have a lot of packages like the systemd
init tests.

Trigger TLPB when the configuration enables per-package directories.

We're using the jlevel argument, which normally is used for BR2_JLEVEL
as the value for calling make -j<N> at the top-level. In fact,
BR2_JLEVEL is "unused" when using TLPB, because the top-level make
acts as the job server that distributes tokens to sub-makes (except
for the few build systems like waf or scons that don't support this),
so it's really the top-level make -j<N> that determines the level of
parallelism, and BR2_JLEVEL doesn't really have an effect.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
[Thomas: extend explanation a bit]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

support/testing/infra/basetest.py

@@ -52,7 +52,7 @@ class BRConfigTest(unittest.TestCase):
 
     def setUp(self):
         self.show_msg("Starting")
-        self.b = Builder(self.config, self.builddir, self.logtofile)
+        self.b = Builder(self.config, self.builddir, self.logtofile, self.jlevel)
 
         if not self.keepbuilds:
             self.b.delete()

support/testing/infra/builder.py

@@ -6,11 +6,12 @@ import infra
 
 
 class Builder(object):
-    def __init__(self, config, builddir, logtofile):
+    def __init__(self, config, builddir, logtofile, jlevel=None):
         self.config = '\n'.join([line.lstrip() for line in
                                  config.splitlines()]) + '\n'
         self.builddir = builddir
         self.logfile = infra.open_log_file(builddir, "build", logtofile)
+        self.jlevel = jlevel
 
     def is_defconfig_valid(self, configfile, defconfig):
         """Check if the .config is contains all lines present in the defconfig."""
@@ -87,6 +88,8 @@ class Builder(object):
         env.update(make_extra_env)
 
         cmd = ["make", "-C", self.builddir]
+        if "BR2_PER_PACKAGE_DIRECTORIES=y" in self.config.splitlines() and self.jlevel:
+            cmd.append(f"-j{self.jlevel}")
         cmd += make_extra_opts
 
         ret = subprocess.call(cmd, stdout=self.logfile, stderr=self.logfile,