gh-150389: Make perf profiler tests resilient

Keep perf test output independent from user perf configuration and
debuginfod, reduce DWARF sample loss, and retry captures only when
expected Python symbols are missing.

Do not fail profiler assertions solely because perf script writes to
stderr.

Closes gh-150395.

Author: pablogsal

Lib/test/test_perf_profiler.py

@@ -34,6 +34,21 @@ def supports_trampoline_profiling():
     raise unittest.SkipTest("perf trampoline profiling not supported")
 
 
+def _perf_env(**env_vars):
+    env = os.environ.copy()
+    # Keep perf's output stable regardless of the builder's perf config.
+    env.update(
+        {
+            "DEBUGINFOD_URLS": "",
+            "PERF_CONFIG": os.devnull,
+        }
+    )
+    if env_vars:
+        env.update(env_vars)
+    env["PYTHON_JIT"] = "0"
+    return env
+
+
 class TestPerfTrampoline(unittest.TestCase):
     def setUp(self):
         super().setUp()
@@ -63,13 +78,12 @@ def baz():
                 """
         with temp_dir() as script_dir:
             script = make_script(script_dir, "perftest", code)
-            env = {**os.environ, "PYTHON_JIT": "0"}
             with subprocess.Popen(
                 [sys.executable, "-Xperf", script],
                 text=True,
                 stderr=subprocess.PIPE,
                 stdout=subprocess.PIPE,
-                env=env,
+                env=_perf_env(),
             ) as process:
                 stdout, stderr = process.communicate()
 
@@ -132,13 +146,12 @@ def baz():
                 """
         with temp_dir() as script_dir:
             script = make_script(script_dir, "perftest", code)
-            env = {**os.environ, "PYTHON_JIT": "0"}
             with subprocess.Popen(
                 [sys.executable, "-Xperf", script],
                 text=True,
                 stderr=subprocess.PIPE,
                 stdout=subprocess.PIPE,
-                env=env,
+                env=_perf_env(),
             ) as process:
                 stdout, stderr = process.communicate()
 
@@ -198,13 +211,12 @@ def test_trampoline_works_after_fork_with_many_code_objects(self):
                 """
         with temp_dir() as script_dir:
             script = make_script(script_dir, "perftest", code)
-            env = {**os.environ, "PYTHON_JIT": "0"}
             with subprocess.Popen(
                 [sys.executable, "-Xperf", script],
                 text=True,
                 stderr=subprocess.PIPE,
                 stdout=subprocess.PIPE,
-                env=env,
+                env=_perf_env(),
             ) as process:
                 stdout, stderr = process.communicate()
 
@@ -242,13 +254,12 @@ def baz():
                 code = set_eval_hook + code
             with temp_dir() as script_dir:
                 script = make_script(script_dir, "perftest", code)
-                env = {**os.environ, "PYTHON_JIT": "0"}
                 with subprocess.Popen(
                     [sys.executable, script],
                     text=True,
                     stderr=subprocess.PIPE,
                     stdout=subprocess.PIPE,
-                    env=env,
+                    env=_perf_env(),
                 ) as process:
                     stdout, stderr = process.communicate()
 
@@ -345,9 +356,12 @@ def perf_command_works():
                 "-c",
                 'print("hello")',
             )
-            env = {**os.environ, "PYTHON_JIT": "0"}
             stdout = subprocess.check_output(
-                cmd, cwd=script_dir, text=True, stderr=subprocess.STDOUT, env=env
+                cmd,
+                cwd=script_dir,
+                text=True,
+                stderr=subprocess.STDOUT,
+                env=_perf_env(),
             )
         except (subprocess.SubprocessError, OSError):
             return False
@@ -359,10 +373,7 @@ def perf_command_works():
 
 
 def run_perf(cwd, *args, use_jit=False, **env_vars):
-    env = os.environ.copy()
-    if env_vars:
-        env.update(env_vars)
-    env["PYTHON_JIT"] = "0"
+    env = _perf_env(**env_vars)
     output_file = cwd + "/perf_output.perf"
     if not use_jit:
         base_cmd = (
@@ -385,6 +396,8 @@ def run_perf(cwd, *args, use_jit=False, **env_vars):
             "--call-graph=dwarf,65528",
             "-F99",
             "-k1",
+            "-m",
+            "4M",
             "-o",
             output_file,
             "--",
@@ -425,54 +438,77 @@ def run_perf(cwd, *args, use_jit=False, **env_vars):
 
 
 class TestPerfProfilerMixin:
-    def run_perf(self, script_dir, perf_mode, script):
+    PERF_CAPTURE_ATTEMPTS = 3
+
+    def run_perf(self, script_dir, script, activate_trampoline=True):
         raise NotImplementedError()
 
+    def run_perf_with_retries(
+        self, script_dir, script, expected_symbols=(), activate_trampoline=True
+    ):
+        stdout = stderr = ""
+        for _ in range(self.PERF_CAPTURE_ATTEMPTS):
+            stdout, stderr = self.run_perf(
+                script_dir, script, activate_trampoline=activate_trampoline
+            )
+            if activate_trampoline and any(
+                symbol not in stdout for symbol in expected_symbols
+            ):
+                continue
+            break
+        return stdout, stderr
+
     def test_python_calls_appear_in_the_stack_if_perf_activated(self):
         with temp_dir() as script_dir:
             code = """if 1:
+                from itertools import repeat
+
                 def foo(n):
-                    x = 0
-                    for i in range(n):
-                        x += i
+                    for _ in repeat(None, n):
+                        pass
 
                 def bar(n):
                     foo(n)
 
                 def baz(n):
                     bar(n)
 
-                baz(10000000)
+                baz(40000000)
                 """
             script = make_script(script_dir, "perftest", code)
-            stdout, stderr = self.run_perf(script_dir, script)
-            self.assertEqual(stderr, "")
+            expected_symbols = [
+                f"py::foo:{script}",
+                f"py::bar:{script}",
+                f"py::baz:{script}",
+            ]
+            stdout, _ = self.run_perf_with_retries(
+                script_dir, script, expected_symbols
+            )
 
-            self.assertIn(f"py::foo:{script}", stdout)
-            self.assertIn(f"py::bar:{script}", stdout)
-            self.assertIn(f"py::baz:{script}", stdout)
+            for expected_symbol in expected_symbols:
+                self.assertIn(expected_symbol, stdout)
 
     def test_python_calls_do_not_appear_in_the_stack_if_perf_deactivated(self):
         with temp_dir() as script_dir:
             code = """if 1:
+                from itertools import repeat
+
                 def foo(n):
-                    x = 0
-                    for i in range(n):
-                        x += i
+                    for _ in repeat(None, n):
+                        pass
 
                 def bar(n):
                     foo(n)
 
                 def baz(n):
                     bar(n)
 
-                baz(10000000)
+                baz(40000000)
                 """
             script = make_script(script_dir, "perftest", code)
-            stdout, stderr = self.run_perf(
+            stdout, _ = self.run_perf_with_retries(
                 script_dir, script, activate_trampoline=False
             )
-            self.assertEqual(stderr, "")
 
             self.assertNotIn(f"py::foo:{script}", stdout)
             self.assertNotIn(f"py::bar:{script}", stdout)
@@ -542,13 +578,12 @@ def compile_trampolines_for_all_functions():
 
         with temp_dir() as script_dir:
             script = make_script(script_dir, "perftest", code)
-            env = {**os.environ, "PYTHON_JIT": "0"}
             with subprocess.Popen(
                 [sys.executable, "-Xperf", script],
                 universal_newlines=True,
                 stderr=subprocess.PIPE,
                 stdout=subprocess.PIPE,
-                env=env,
+                env=_perf_env(),
             ) as process:
                 stdout, stderr = process.communicate()