feat: skip Python runtime objects in callgrind

src/pytest_codspeed/instruments/hooks/__init__.py

@@ -50,6 +50,10 @@ def __init__(self) -> None:
         if SUPPORTS_PERF_TRAMPOLINE and not sys.is_stack_trampoline_active():
             sys.activate_stack_trampoline("perf")  # type: ignore
 
+        # Ignore libpython and python executable frames in callgrind so they
+        # don't obfuscate the flamegraph.
+        callgrind_skip_python_runtime()
+
     def __del__(self):
         # Don't manually deinit - let the capsule destructor handle it
         pass
@@ -223,3 +227,47 @@ def collect_and_write_python_environment(self) -> None:
         self.set_environment_list(section, "config", config_items)
 
         self.write_environment()
+
+
+def callgrind_add_obj_skip(path: str) -> None:
+    """Tell callgrind to skip the given object file (and its realpath).
+
+    The actual Valgrind client-request trapdoor lives in the C extension; this
+    just resolves the realpath so callgrind's strcmp matches either form.
+    """
+    if not path or not os.path.exists(path):
+        return
+    try:
+        from . import dist_instrument_hooks  # type: ignore
+    except ImportError:
+        return
+
+    dist_instrument_hooks.callgrind_add_obj_skip(path.encode())
+
+    # The dynamic loader maps the realpath (e.g. libpython3.12.so.1.0), and
+    # callgrind stores that in obj_node->name. Skip both so the exact strcmp
+    # matches regardless of which path callgrind sees.
+    real = os.path.realpath(path)
+    if real != path:
+        dist_instrument_hooks.callgrind_add_obj_skip(real.encode())
+
+
+def callgrind_skip_python_runtime() -> None:
+    """Skip libpython and the python executable from callgrind measurement."""
+    ldlibrary = sysconfig.get_config_var("LDLIBRARY")
+    libdir = sysconfig.get_config_var("LIBDIR")
+    libpython = next(
+        (
+            p
+            for p in (
+                os.path.join(libdir, ldlibrary) if ldlibrary and libdir else None,
+                os.path.join(sys.prefix, "lib", ldlibrary) if ldlibrary else None,
+            )
+            if p and os.path.exists(p)
+        ),
+        None,
+    )
+    if libpython:
+        callgrind_add_obj_skip(libpython)
+
+    callgrind_add_obj_skip(sys.executable)

src/pytest_codspeed/instruments/hooks/instrument_hooks_module.c

@@ -1,6 +1,12 @@
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include "core.h"
+#include "valgrind.h"
+
+/* CodSpeed-specific Valgrind client request: tell callgrind to skip an
+ * object file by path. Not present in upstream callgrind.h. */
+// TODO(COD-2654): Move this to instrument-hooks and just call it here
+#define VG_USERREQ__ADD_OBJ_SKIP 0x43540006
 
 /* Capsule destructor for InstrumentHooks pointer */
 static void instrument_hooks_capsule_destructor(PyObject *capsule) {
@@ -242,6 +248,17 @@ static PyObject *py_instrument_hooks_write_environment(PyObject *self, PyObject
     return PyLong_FromLong(result);
 }
 
+/* callgrind_add_obj_skip(path: bytes) -> None
+ * Outside Valgrind this expands to a nop, so it's safe on bare metal. */
+static PyObject *py_callgrind_add_obj_skip(PyObject *self, PyObject *args) {
+    const char *path;
+    if (!PyArg_ParseTuple(args, "y", &path)) {
+        return NULL;
+    }
+    VALGRIND_DO_CLIENT_REQUEST_STMT(VG_USERREQ__ADD_OBJ_SKIP, path, 0, 0, 0, 0);
+    Py_RETURN_NONE;
+}
+
 /* Method definitions */
 static PyMethodDef InstrumentHooksMethods[] = {
     {"instrument_hooks_init", py_instrument_hooks_init, METH_NOARGS,
@@ -272,6 +289,8 @@ static PyMethodDef InstrumentHooksMethods[] = {
      "Register a list of values under a named section for environment collection."},
     {"instrument_hooks_write_environment", py_instrument_hooks_write_environment, METH_VARARGS,
      "Flush all registered environment sections to disk."},
+    {"callgrind_add_obj_skip", py_callgrind_add_obj_skip, METH_VARARGS,
+     "Tell callgrind to skip the given object file path."},
     {NULL, NULL, 0, NULL}
 };