[PATCH v20 21/21] perf python: Add LiveSession helper

[Ian Rogers]

Add LiveSession class in tools/perf/python/perf_live.py to support
live event collection using perf.evlist and perf.parse_events,
avoiding the need to fork a separate perf record process.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
Assisted-by: Gemini:gemini-3.1-pro-preview
---
 tools/perf/python/perf_live.py             | 59 ++++++++++++++++++++++
 tools/perf/tests/shell/lib/setup_python.sh | 13 +++++
 2 files changed, 72 insertions(+)
 create mode 100755 tools/perf/python/perf_live.py

diff --git a/tools/perf/python/perf_live.py b/tools/perf/python/perf_live.py
new file mode 100755
index 000000000000..616b5f657463
--- /dev/null
+++ b/tools/perf/python/perf_live.py
@@ -0,0 +1,59 @@
+# SPDX-License-Identifier: GPL-2.0
+"""
+Live event session helper using perf.evlist.
+
+This module provides a LiveSession class that allows running a callback
+for each event collected live from the system, similar to perf.session
+but without requiring a perf.data file.
+"""
+
+import perf
+
+
+class LiveSession:
+    """Represents a live event collection session."""
+
+    def __init__(self, event_string: str, sample_callback):
+        self.event_string = event_string
+        self.sample_callback = sample_callback
+        # Create a cpu map for all online CPUs
+        self.cpus = perf.cpu_map()
+        # Parse events and set maps
+        self.evlist = perf.parse_events(self.event_string, self.cpus)
+        self.evlist.config()
+
+    def run(self):
+        """Run the live session."""
+        try:
+            self.evlist.open()
+            self.evlist.mmap()
+            self.evlist.enable()
+
+            while True:
+                # Poll for events with 100ms timeout
+                try:
+                    self.evlist.poll(100)
+                except InterruptedError:
+                    continue
+                for cpu in self.cpus:
+                    for _ in range(1000): # Limit to 1000 events per CPU per poll to prevent starvation
+                        try:
+                            event = self.evlist.read_on_cpu(cpu)
+                        except TypeError as e:
+                            if "Unknown CPU" in str(e):
+                                # CPU might be unmapped or offline, wait for mmap event
+                                break
+                            if "Unexpected header type" in str(e):
+                                # Ignore valid but unsupported event types
+                                continue
+                            raise
+
+                        if event is None:
+                            break
+
+                        if event.type == perf.RECORD_SAMPLE:
+                            self.sample_callback(event)
+        except KeyboardInterrupt:
+            pass
+        finally:
+            self.evlist.close()
diff --git a/tools/perf/tests/shell/lib/setup_python.sh b/tools/perf/tests/shell/lib/setup_python.sh
index a58e5536f2ed..2173215a0517 100644
--- a/tools/perf/tests/shell/lib/setup_python.sh
+++ b/tools/perf/tests/shell/lib/setup_python.sh
@@ -14,3 +14,16 @@ then
   echo Skipping test, python not detected please set environment variable PYTHON.
   exit 2
 fi
+
+# Set PYTHONPATH to find the in-tree built perf.so first, avoiding system-wide perf.so
+if [ -n "$PERF_EXEC_PATH" ] && [ -d "$PERF_EXEC_PATH/python" ]; then
+  PYTHONPATH_DIR="$PERF_EXEC_PATH/python"
+elif [ -d "$(dirname "$0")/../../python" ]; then
+  PYTHONPATH_DIR="$(dirname "$0")/../../python"
+elif [ -d "$(dirname "$0")/../python" ]; then
+  PYTHONPATH_DIR="$(dirname "$0")/../python"
+fi
+
+if [ -n "$PYTHONPATH_DIR" ]; then
+  export PYTHONPATH="$PYTHONPATH_DIR${PYTHONPATH:+:$PYTHONPATH}"
+fi
-- 
2.54.0.1136.gdb2ca164c4-goog