perf python: Add LiveSession helper

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@google.com>
Assisted-by: Gemini:gemini-3.1-pro-preview
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alice Rogers <alice.mei.rogers@gmail.com>
Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Leo Yan <leo.yan@linux.dev>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

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()

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