Run test_asyncio and test_compiler sub-tests in parallel

Summary:
These two tests are typically the long-poles in runs because they are modules with a lot of further sub-tests run serially. By breaking out the sub-tests as independent modules we can run a lot more in parallel.

The real win comes in the next diff but with this change alone on my devserver:
* With a debug build:
  * `time make testcinder` goes from ~25m -> ~19m.
  * `time make testcinder_jit` goes from ~26m -> ~18m.
* With a release build:
  * `time make testcinder` goes from ~6m15s -> ~4m45s.
  * `time make testcinder_jit` goes from ~6m -> ~5m30s.

While this is a bit hacky and annoyingly involves changing CPython test infra, I think the maintenance overhead is worth it. It's not a complicated change and I think the win in productivity with the diff above is significant.

Reviewed By: sinancepel

Differential Revision: D35383641

fbshipit-source-id: eaacb81

Lib/test/libregrtest/runtest.py

@@ -61,6 +61,14 @@
 # set of tests that we don't want to be executed when using regrtest
 NOTTESTS = set()
 
+# If these test directories are encountered recurse into them and treat each
+# test_ .py or dir as a separate test module. This can increase parallelism.
+# Beware this can't generally be done for any directory with sub-tests as the
+# __init__.py may do things which alter what tests are to be run.
+SPLITTESTDIRS = {
+    "test_asyncio",
+    "test_compiler",
+}
 
 # used by --findleaks, store for gc.garbage
 FOUND_GARBAGE = []
@@ -87,16 +95,30 @@ def findtestdir(path=None):
     return path or os.path.dirname(os.path.dirname(__file__)) or os.curdir
 
 
-def findtests(testdir=None, stdtests=STDTESTS, nottests=NOTTESTS):
+def findtests(
+    testdir=None,
+    stdtests=STDTESTS,
+    nottests=NOTTESTS,
+    splittestdirs=SPLITTESTDIRS,
+    base_mod="",
+):
     """Return a list of all applicable test modules."""
     testdir = findtestdir(testdir)
     names = os.listdir(testdir)
     tests = []
     others = set(stdtests) | nottests
     for name in names:
         mod, ext = os.path.splitext(name)
-        if mod[:5] == "test_" and ext in (".py", "") and mod not in others:
-            tests.append(mod)
+        if mod[:5] == "test_" and mod not in others:
+            if mod in splittestdirs:
+                subdir = os.path.join(testdir, mod)
+                if len(base_mod):
+                    mod = f"{base_mod}.{mod}"
+                else:
+                    mod = f"test.{mod}"
+                tests.extend(findtests(subdir, [], nottests, splittestdirs, mod))
+            elif ext in (".py", ""):
+                tests.append(f"{base_mod}.{mod}" if len(base_mod) else mod)
     return stdtests + sorted(tests)
 
 

Lib/test/test_asyncio/test_sock_lowlevel.py

@@ -7,6 +7,10 @@
 from test import support
 
 
+def tearDownModule():
+    asyncio.set_event_loop_policy(None)
+
+
 class MyProto(asyncio.Protocol):
     connected = None
     done = None