diff --git a/Lib/test/libregrtest/cmdline.py b/Lib/test/libregrtest/cmdline.py

index 538ff05..e7f2013 100644

--- a/Lib/test/libregrtest/cmdline.py

+++ b/Lib/test/libregrtest/cmdline.py

@@ -263,7 +263,9 @@ def _create_parser():

                        help='only write the name of test cases that will be run'

                             ' , don\'t execute them')

     group.add_argument('-P', '--pgo', dest='pgo', action='store_true',

-                       help='enable Profile Guided Optimization training')

+                       help='enable Profile Guided Optimization (PGO) training')

+    group.add_argument('--pgo-extended', action='store_true',

+                       help='enable extended PGO training (slower training)')

     group.add_argument('--fail-env-changed', action='store_true',

                        help='if a test file alters the environment, mark '

                             'the test as failed')

@@ -339,6 +341,8 @@ def _parse_args(args, **kwargs):

         parser.error("-G/--failfast needs either -v or -W")

     if ns.pgo and (ns.verbose or ns.verbose2 or ns.verbose3):

         parser.error("--pgo/-v don't go together!")

+    if ns.pgo_extended:

+        ns.pgo = True  # pgo_extended implies pgo

     if ns.nowindows:

         print("Warning: the --nowindows (-n) option is deprecated. "

diff --git a/Lib/test/libregrtest/main.py b/Lib/test/libregrtest/main.py

index b6d05f6..524dbfa 100644

--- a/Lib/test/libregrtest/main.py

+++ b/Lib/test/libregrtest/main.py

@@ -17,6 +17,7 @@ from test.libregrtest.runtest import (

     INTERRUPTED, CHILD_ERROR, TEST_DID_NOT_RUN,

     PROGRESS_MIN_TIME, format_test_result)

 from test.libregrtest.setup import setup_tests

+from test.libregrtest.pgo import setup_pgo_tests

 from test.libregrtest.utils import removepy, count, format_duration, printlist

 from test import support

 try:

@@ -214,6 +215,10 @@ class Regrtest:

         removepy(self.tests)

+        if self.ns.pgo:

+            # add default PGO tests if no tests are specified

+            setup_pgo_tests(self.ns)

+

         stdtests = STDTESTS[:]

         nottests = NOTTESTS.copy()

         if self.ns.exclude:

@@ -601,6 +606,7 @@ class Regrtest:

             input("Press any key to continue...")

         support.PGO = self.ns.pgo

+        support.PGO_EXTENDED = self.ns.pgo_extended

         setup_tests(self.ns)

diff --git a/Lib/test/libregrtest/pgo.py b/Lib/test/libregrtest/pgo.py

new file mode 100644

index 0000000..379ff05

--- /dev/null

+++ b/Lib/test/libregrtest/pgo.py

@@ -0,0 +1,55 @@

+# Set of tests run by default if --pgo is specified.  The tests below were

+# chosen based on the following criteria: either they exercise a commonly used

+# C extension module or type, or they run some relatively typical Python code.

+# Long running tests should be avoided because the PGO instrumented executable

+# runs slowly.

+PGO_TESTS = [

+    'test_array',

+    'test_base64',

+    'test_binascii',

+    'test_binop',

+    'test_bisect',

+    'test_bytes',

+    'test_bz2',

+    'test_cmath',

+    'test_codecs',

+    'test_collections',

+    'test_complex',

+    'test_dataclasses',

+    'test_datetime',

+    'test_decimal',

+    'test_difflib',

+    'test_embed',

+    'test_float',

+    'test_fstring',

+    'test_functools',

+    'test_generators',

+    'test_hashlib',

+    'test_heapq',

+    'test_int',

+    'test_itertools',

+    'test_json',

+    'test_long',

+    'test_lzma',

+    'test_math',

+    'test_memoryview',

+    'test_operator',

+    'test_ordered_dict',

+    'test_pickle',

+    'test_pprint',

+    'test_re',

+    'test_set',

+    'test_sqlite',

+    'test_statistics',

+    'test_struct',

+    'test_tabnanny',

+    'test_time',

+    'test_unicode',

+    'test_xml_etree',

+    'test_xml_etree_c',

+]

+

+def setup_pgo_tests(ns):

+    if not ns.args and not ns.pgo_extended:

+        # run default set of tests for PGO training

+        ns.args = PGO_TESTS[:]

diff --git a/Lib/test/pickletester.py b/Lib/test/pickletester.py

index 764057a..468ee46 100644

--- a/Lib/test/pickletester.py

+++ b/Lib/test/pickletester.py

@@ -2039,6 +2039,7 @@ class AbstractPickleTests(unittest.TestCase):

     FRAME_SIZE_TARGET = 64 * 1024

+    @support.skip_if_pgo_task

     def check_frame_opcodes(self, pickled):

         """

         Check the arguments of FRAME opcodes in a protocol 4+ pickle.

@@ -2059,6 +2060,7 @@ class AbstractPickleTests(unittest.TestCase):

         frame_size = len(pickled) - last_pos - frame_opcode_size

         self.assertEqual(frame_size, last_arg)

+    @support.skip_if_pgo_task

     def test_framing_many_objects(self):

         obj = list(range(10**5))

         for proto in range(4, pickle.HIGHEST_PROTOCOL + 1):

diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py

index 66c0fed..e80a819 100644

--- a/Lib/test/support/__init__.py

+++ b/Lib/test/support/__init__.py

@@ -953,6 +953,10 @@ SAVEDCWD = os.getcwd()

 # useful for PGO

 PGO = False

+# Set by libregrtest/main.py if we are running the extended (time consuming)

+# PGO task.  If this is True, PGO is also True.

+PGO_EXTENDED = False

+

 @contextlib.contextmanager

 def temp_dir(path=None, quiet=False):

     """Return a context manager that creates a temporary directory.

@@ -2442,6 +2446,11 @@ def skip_unless_xattr(test):

     msg = "no non-broken extended attribute support"

     return test if ok else unittest.skip(msg)(test)

+def skip_if_pgo_task(test):

+    """Skip decorator for tests not run in (non-extended) PGO task"""

+    ok = not PGO or PGO_EXTENDED

+    msg = "Not run for (non-extended) PGO task"

+    return test if ok else unittest.skip(msg)(test)

 def fs_is_case_insensitive(directory):

     """Detects if the file system for the specified directory is case-insensitive."""

diff --git a/Lib/test/test_bz2.py b/Lib/test/test_bz2.py

index f340f23..ebb151c 100644

--- a/Lib/test/test_bz2.py

+++ b/Lib/test/test_bz2.py

@@ -654,6 +654,7 @@ class BZ2CompressorTest(BaseTest):

         data += bz2c.flush()

         self.assertEqual(ext_decompress(data), self.TEXT)

+    @support.skip_if_pgo_task

     @bigmemtest(size=_4G + 100, memuse=2)

     def testCompress4G(self, size):

         # "Test BZ2Compressor.compress()/flush() with >4GiB input"

@@ -712,6 +713,7 @@ class BZ2DecompressorTest(BaseTest):

         self.assertRaises(EOFError, bz2d.decompress, b"anything")

         self.assertRaises(EOFError, bz2d.decompress, b"")

+    @support.skip_if_pgo_task

     @bigmemtest(size=_4G + 100, memuse=3.3)

     def testDecompress4G(self, size):

         # "Test BZ2Decompressor.decompress() with >4GiB input"

diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py

index 9317951..8c1d016 100644

--- a/Lib/test/test_itertools.py

+++ b/Lib/test/test_itertools.py

@@ -2023,6 +2023,7 @@ class RegressionTests(unittest.TestCase):

         self.assertRaises(AssertionError, list, cycle(gen1()))

         self.assertEqual(hist, [0,1])

+    @support.skip_if_pgo_task

     def test_long_chain_of_empty_iterables(self):

         # Make sure itertools.chain doesn't run into recursion limits when

         # dealing with long chains of empty iterables. Even with a high

diff --git a/Lib/test/test_lzma.py b/Lib/test/test_lzma.py

index 3dc2c1e..117de0a 100644

--- a/Lib/test/test_lzma.py

+++ b/Lib/test/test_lzma.py

@@ -333,6 +333,7 @@ class CompressorDecompressorTestCase(unittest.TestCase):

     # Test with inputs larger than 4GiB.

+    @support.skip_if_pgo_task

     @bigmemtest(size=_4G + 100, memuse=2)

     def test_compressor_bigmem(self, size):

         lzc = LZMACompressor()

@@ -344,6 +345,7 @@ class CompressorDecompressorTestCase(unittest.TestCase):

         finally:

             ddata = None

+    @support.skip_if_pgo_task

     @bigmemtest(size=_4G + 100, memuse=3)

     def test_decompressor_bigmem(self, size):

         lzd = LZMADecompressor()

diff --git a/Lib/test/test_regrtest.py b/Lib/test/test_regrtest.py

index 5347bb1..9d83217 100644

--- a/Lib/test/test_regrtest.py

+++ b/Lib/test/test_regrtest.py

@@ -6,6 +6,7 @@ Note: test_regrtest cannot be run twice in parallel.

 import contextlib

 import faulthandler

+import glob

 import io

 import os.path

 import platform

@@ -532,6 +533,31 @@ class BaseTestCase(unittest.TestCase):

         return proc.stdout

+class CheckActualTests(BaseTestCase):

+    """

+    Check that regrtest appears to find the expected set of tests.

+    """

+

+    def test_finds_expected_number_of_tests(self):

+        args = ['-Wd', '-E', '-bb', '-m', 'test.regrtest', '--list-tests']

+        output = self.run_python(args)

+        rough_number_of_tests_found = len(output.splitlines())

+        actual_testsuite_glob = os.path.join(os.path.dirname(__file__),

+                                             'test*.py')

+        rough_counted_test_py_files = len(glob.glob(actual_testsuite_glob))

+        # We're not trying to duplicate test finding logic in here,

+        # just give a rough estimate of how many there should be and

+        # be near that.  This is a regression test to prevent mishaps

+        # such as https://bugs.python.org/issue37667 in the future.

+        # If you need to change the values in here during some

+        # mythical future test suite reorganization, don't go

+        # overboard with logic and keep that goal in mind.

+        self.assertGreater(rough_number_of_tests_found,

+                           rough_counted_test_py_files*9//10,

+                           msg='Unexpectedly low number of tests found in:\n'

+                           f'{", ".join(output.splitlines())}')

+

+

 class ProgramsTestCase(BaseTestCase):

     """

     Test various ways to run the Python test suite. Use options close

diff --git a/Makefile.pre.in b/Makefile.pre.in

index b452289..cc428ac 100644

--- a/Makefile.pre.in

+++ b/Makefile.pre.in

@@ -247,9 +247,10 @@ TCLTK_INCLUDES=	@TCLTK_INCLUDES@

 TCLTK_LIBS=	@TCLTK_LIBS@

 # The task to run while instrumented when building the profile-opt target.

-# We exclude unittests with -x that take a rediculious amount of time to

-# run in the instrumented training build or do not provide much value.

-PROFILE_TASK=-m test.regrtest --pgo

+# To speed up profile generation, we don't run the full unit test suite

+# by default. The default is "-m test --pgo". To run more tests, use

+# PROFILE_TASK="-m test --pgo-extended"

+PROFILE_TASK=	@PROFILE_TASK@

 # report files for gcov / lcov coverage report

 COVERAGE_INFO=	$(abs_builddir)/coverage.info

diff --git a/configure.ac b/configure.ac

index c071ec3..816fc5a 100644

--- a/configure.ac

+++ b/configure.ac

@@ -1308,6 +1308,14 @@ else

   DEF_MAKE_RULE="all"

 fi

+AC_ARG_VAR(PROFILE_TASK, Python args for PGO generation task)

+AC_MSG_CHECKING(PROFILE_TASK)

+if test -z "$PROFILE_TASK"

+then

+	PROFILE_TASK='-m test --pgo'

+fi

+AC_MSG_RESULT($PROFILE_TASK)

+

 # Make llvm-relatec checks work on systems where llvm tools are not installed with their

 # normal names in the default $PATH (ie: Ubuntu).  They exist under the

 # non-suffixed name in their versioned llvm directory.