[lit] Sort test start times based on prior test timing data

Lit as it exists today has three hacks that allow users to run tests earlier:

1) An entire test suite can set the `is_early` boolean.
2) A very recently introduced "early_tests" feature.
3) The `--incremental` flag forces failing tests to run first.

All of these approaches have problems.

1) The `is_early` feature was until very recently undocumented. Nevertheless it still lacks testing and is a imprecise way of optimizing test starting times.
2) The `early_tests` feature requires manual updates and doesn't scale.
3) `--incremental` is undocumented, untested, and it requires modifying the *source* file system by "touching" the file. This "touch" based approach is arguably a hack because it confuses editors (because it looks like the test was modified behind the back of the editor) and "touching" the test source file doesn't work if the test suite is read only from the perspective of `lit` (via advanced filesystem/build tricks).

This patch attempts to simplify and address all of the above problems.

This patch formalizes, documents, tests, and defaults lit to recording the execution time of tests and then reordering all tests during the next execution. By reordering the tests, high core count machines run faster, sometimes significantly so.

This patch also always runs failing tests first, which is a positive user experience win for those that didn't know about the hidden `--incremental` flag.

Finally, if users want, they can _optionally_ commit the test timing data (or a subset thereof) back to the repository to accelerate bots and first-time runs of the test suite.

Reviewed By: jhenderson, yln

Differential Revision: https://reviews.llvm.org/D98179

docs/CommandGuide/lit.rst

@@ -20,7 +20,7 @@ user interface as possible.
 command line.  Tests can be either individual test files or directories to
 search for tests (see :ref:`test-discovery`).
 
-Each specified test will be executed (potentially in parallel) and once all
+Each specified test will be executed (potentially concurrently) and once all
 tests have been run :program:`lit` will print summary information on the number
 of tests which passed or failed (see :ref:`test-status-results`).  The
 :program:`lit` program will execute with a non-zero exit code if any tests
@@ -151,8 +151,7 @@ EXECUTION OPTIONS
 
  Track the wall time individual tests take to execute and includes the results
  in the summary output.  This is useful for determining which tests in a test
- suite take the most time to execute.  Note that this option is most useful
- with ``-j 1``.
+ suite take the most time to execute.
 
 .. option:: --ignore-fail
 
@@ -168,6 +167,17 @@ EXECUTION OPTIONS
 SELECTION OPTIONS
 -----------------
 
+By default, `lit` will run failing tests first, then run tests in descending
+execution time order to optimize concurrency.
+
+The timing data is stored in the `test_exec_root` in a file named
+`.lit_test_times.txt`. If this file does not exist, then `lit` checks the
+`test_source_root` for the file to optionally accelerate clean builds.
+
+.. option:: --shuffle
+
+ Run the tests in a random order, not failing/slowest first.
+
 .. option:: --max-failures N
 
  Stop execution after the given number ``N`` of failures.
@@ -201,10 +211,6 @@ SELECTION OPTIONS
  must be in the range ``1..M``. The environment variable
  ``LIT_RUN_SHARD`` can also be used in place of this option.
 
-.. option:: --shuffle
-
- Run the tests in a random order.
-
 .. option:: --timeout=N
 
  Spend at most ``N`` seconds (approximately) running each individual test.
@@ -416,13 +422,6 @@ executed, two important global variables are predefined:
  **root** The root configuration.  This is the top-most :program:`lit` configuration in
  the project.
 
- **is_early** Whether the test suite as a whole should be given a head start
- before other test suites run.
-
- **early_tests** An explicit set of '/' separated test paths that should be
- given a head start before other tests run. For example, the top five or so
- slowest tests. See also: `--time-tests`
-
  **pipefail** Normally a test using a shell pipe fails if any of the commands
  on the pipe fail. If this is not desired, setting this variable to false
  makes the test fail only if the last command in the pipe fails.

test/Unit/lit.cfg.py

@@ -13,9 +13,6 @@ config.name = 'LLVM-Unit'
 # suffixes: A list of file extensions to treat as test files.
 config.suffixes = []
 
-# is_early; Request to run this suite early.
-config.is_early = True
-
 # test_source_root: The root path where tests are located.
 # test_exec_root: The root path where tests should be run.
 config.test_exec_root = os.path.join(config.llvm_obj_root, 'unittests')

utils/lit/lit/Test.py

@@ -207,6 +207,16 @@ class TestSuite:
         # The test suite configuration.
         self.config = config
 
+        self.test_times = {}
+        test_times_file = os.path.join(exec_root, '.lit_test_times.txt')
+        if not os.path.exists(test_times_file):
+            test_times_file = os.path.join(source_root, '.lit_test_times.txt')
+        if os.path.exists(test_times_file):
+            with open(test_times_file, 'r') as time_file:
+                for line in time_file:
+                    time, path = line.split(maxsplit=1)
+                    self.test_times[path.strip('\n')] = float(time)
+
     def getSourcePath(self, components):
         return os.path.join(self.source_root, *components)
 
@@ -246,6 +256,18 @@ class Test:
         # The test result, once complete.
         self.result = None
 
+        # The previous test failure state, if applicable.
+        self.previous_failure = False
+
+        # The previous test elapsed time, if applicable.
+        self.previous_elapsed = 0.0
+
+        if os.sep.join(path_in_suite) in suite.test_times:
+            time = suite.test_times[os.sep.join(path_in_suite)]
+            self.previous_elapsed = abs(time)
+            self.previous_failure = time < 0
+
+
     def setResult(self, result):
         assert self.result is None, "result already set"
         assert isinstance(result, Result), "unexpected result type"
@@ -395,15 +417,3 @@ class Test:
         )
         identifiers = set(filter(BooleanExpression.isIdentifier, tokens))
         return identifiers
-
-    def isEarlyTest(self):
-        """
-        isEarlyTest() -> bool
-
-        Check whether this test should be executed early in a particular run.
-        This can be used for test suites with long running tests to maximize
-        parallelism or where it is desirable to surface their failures early.
-        """
-        if '/'.join(self.path_in_suite) in self.suite.config.early_tests:
-            return True
-        return self.suite.config.is_early

utils/lit/lit/TestingConfig.py

@@ -125,10 +125,6 @@ class TestingConfig(object):
         # require one of the features in this list if this list is non-empty.
         # Configurations can set this list to restrict the set of tests to run.
         self.limit_to_features = set(limit_to_features)
-        # Whether the suite should be tested early in a given run.
-        self.is_early = bool(is_early)
-        # List of tests to run early.
-        self.early_tests = {}
         self.parallelism_group = parallelism_group
         self._recursiveExpansionLimit = None
 

utils/lit/lit/cl_arguments.py

@@ -9,8 +9,7 @@ import lit.util
 
 
 class TestOrder(enum.Enum):
-    EARLY_TESTS_THEN_BY_NAME = enum.auto()
-    FAILING_FIRST = enum.auto()
+    DEFAULT = enum.auto()
     RANDOM = enum.auto()
 
 
@@ -155,7 +154,7 @@ def parse_args():
             help="Run tests in random order",
             action="store_true")
     selection_group.add_argument("-i", "--incremental",
-            help="Run modified and failing tests first (updates mtimes)",
+            help="Run failed tests first (DEPRECATED: now always enabled)",
             action="store_true")
     selection_group.add_argument("--filter",
             metavar="REGEX",
@@ -208,12 +207,13 @@ def parse_args():
     if opts.echoAllCommands:
         opts.showOutput = True
 
+    if opts.incremental:
+        print('WARNING: --incremental is deprecated. Failing tests now always run first.')
+
     if opts.shuffle:
         opts.order = TestOrder.RANDOM
-    elif opts.incremental:
-        opts.order = TestOrder.FAILING_FIRST
     else:
-        opts.order = TestOrder.EARLY_TESTS_THEN_BY_NAME
+        opts.order = TestOrder.DEFAULT
 
     if opts.numShards or opts.runShard:
         if not opts.numShards or not opts.runShard:

utils/lit/lit/discovery.py

@@ -281,6 +281,11 @@ def find_tests_for_inputs(lit_config, inputs, indirectlyRunCheck):
         if prev == len(tests):
             lit_config.warning('input %r contained no tests' % input)
 
+    # This data is no longer needed but keeping it around causes awful
+    # performance problems while the test suites run.
+    for k, suite in test_suite_cache.items():
+      suite[0].test_times = None
+
     # If there were any errors during test discovery, exit now.
     if lit_config.numErrors:
         sys.stderr.write('%d errors, exiting.\n' % lit_config.numErrors)

utils/lit/lit/main.py

@@ -105,6 +105,8 @@ def main(builtin_params={}):
     run_tests(selected_tests, lit_config, opts, len(discovered_tests))
     elapsed = time.time() - start
 
+    record_test_times(selected_tests, lit_config)
+
     if opts.time_tests:
         print_histogram(discovered_tests)
 
@@ -163,20 +165,12 @@ def print_discovered(tests, show_suites, show_tests):
 
 def determine_order(tests, order):
     from lit.cl_arguments import TestOrder
-    if order == TestOrder.EARLY_TESTS_THEN_BY_NAME:
-        tests.sort(key=lambda t: (not t.isEarlyTest(), t.getFullName()))
-    elif order == TestOrder.FAILING_FIRST:
-        def by_mtime(test):
-            return os.path.getmtime(test.getFilePath())
-        tests.sort(key=by_mtime, reverse=True)
-    elif order == TestOrder.RANDOM:
+    if order == TestOrder.RANDOM:
         import random
         random.shuffle(tests)
-
-
-def touch_file(test):
-    if test.isFailure():
-        os.utime(test.getFilePath(), None)
+    else:
+        assert order == TestOrder.DEFAULT, 'Unknown TestOrder value'
+        tests.sort(key=lambda t: (not t.previous_failure, -t.previous_elapsed, t.getFullName()))
 
 
 def filter_by_shard(tests, run, shards, lit_config):
@@ -213,12 +207,7 @@ def run_tests(tests, lit_config, opts, discovered_tests):
     display = lit.display.create_display(opts, len(tests), discovered_tests,
                                          workers)
 
-    def progress_callback(test):
-        display.update(test)
-        if opts.order == lit.cl_arguments.TestOrder.FAILING_FIRST:
-            touch_file(test)
-
-    run = lit.run.Run(tests, lit_config, workers, progress_callback,
+    run = lit.run.Run(tests, lit_config, workers, display.update,
                       opts.max_failures, opts.timeout)
 
     display.print_header()
@@ -267,6 +256,27 @@ def execute_in_tmp_dir(run, lit_config):
                 lit_config.warning("Failed to delete temp directory '%s', try upgrading your version of Python to fix this" % tmp_dir)
 
 
+def record_test_times(tests, lit_config):
+    times_by_suite = {}
+    for t in tests:
+        if not t.result.elapsed:
+            continue
+        if not t.suite.exec_root in times_by_suite:
+            times_by_suite[t.suite.exec_root] = []
+        time = -t.result.elapsed if t.isFailure() else t.result.elapsed
+        times_by_suite[t.suite.exec_root].append((os.sep.join(t.path_in_suite), t.result.elapsed))
+
+    for s, value in times_by_suite.items():
+        try:
+            path = os.path.join(s, '.lit_test_times.txt')
+            with open(path, 'w') as time_file:
+                for name, time in value:
+                    time_file.write(("%e" % time) + ' ' + name + '\n')
+        except:
+            lit_config.warning('Could not save test time: ' + path)
+            continue
+
+
 def print_histogram(tests):
     test_times = [(t.getFullName(), t.result.elapsed)
                   for t in tests if t.result.elapsed]

utils/lit/tests/Inputs/reorder/.lit_test_times.txt

@@ -0,0 +1,3 @@
+3.0 subdir/ccc.txt
+2.0 bbb.txt
+0.1 aaa.txt

utils/lit/tests/Inputs/reorder/lit.cfg

@@ -1,7 +1,6 @@
 import lit.formats
-config.name = 'early-tests'
+config.name = 'reorder'
 config.suffixes = ['.txt']
 config.test_format = lit.formats.ShTest()
 config.test_source_root = None
 config.test_exec_root = None
-config.early_tests = { "subdir/ccc.txt" }

utils/lit/tests/early-tests.py

@@ -1,9 +0,0 @@
-## Check that we can run tests early.
-
-# RUN: %{lit} -j1 %{inputs}/early-tests | FileCheck %s
-
-# CHECK:     -- Testing: 3 tests, 1 workers --
-# CHECK-NEXT: PASS: early-tests :: subdir/ccc.txt
-# CHECK-NEXT: PASS: early-tests :: aaa.txt
-# CHECK-NEXT: PASS: early-tests :: bbb.txt
-# CHECK:     Passed: 3

utils/lit/tests/ignore-fail.py

@@ -6,10 +6,10 @@
 
 # END.
 
-# CHECK: FAIL: ignore-fail :: fail.txt
-# CHECK: UNRESOLVED: ignore-fail :: unresolved.txt
-# CHECK: XFAIL: ignore-fail :: xfail.txt
-# CHECK: XPASS: ignore-fail :: xpass.txt
+# CHECK-DAG: FAIL: ignore-fail :: fail.txt
+# CHECK-DAG: UNRESOLVED: ignore-fail :: unresolved.txt
+# CHECK-DAG: XFAIL: ignore-fail :: xfail.txt
+# CHECK-DAG: XPASS: ignore-fail :: xpass.txt
 
 #      CHECK: Testing Time:
 # CHECK-NEXT:   Expectedly Failed : 1

utils/lit/tests/reorder.py

@@ -0,0 +1,12 @@
+## Check that we can reorder test runs.
+
+# RUN: cp %{inputs}/reorder/.lit_test_times.txt %{inputs}/reorder/.lit_test_times.txt.orig
+# RUN: %{lit} -j1 %{inputs}/reorder | FileCheck %s
+# RUN: not diff %{inputs}/reorder/.lit_test_times.txt %{inputs}/reorder/.lit_test_times.txt.orig
+# END.
+
+# CHECK:     -- Testing: 3 tests, 1 workers --
+# CHECK-NEXT: PASS: reorder :: subdir/ccc.txt
+# CHECK-NEXT: PASS: reorder :: bbb.txt
+# CHECK-NEXT: PASS: reorder :: aaa.txt
+# CHECK:     Passed: 3

utils/lit/tests/shtest-shell.py

@@ -8,6 +8,8 @@
 #
 # Test again in non-UTF shell to catch potential errors with python 2 seen
 # on stdout-encoding.txt
+# FIXME: lit's testing sets source_root == exec_root which complicates running lit more than once per test.
+# RUN: rm -f %{inputs}/shtest-shell/.lit_test_times.txt
 # RUN: env PYTHONIOENCODING=ascii not %{lit} -j 1 -a %{inputs}/shtest-shell > %t.ascii.out
 # FIXME: Temporarily dump test output so we can debug failing tests on
 # buildbots.