perf script: Add -e option to flamegraph script

When processing the perf data file generated with multiple events,
the flamegraph script will count all the events regardless of
different event names.

This patch tries to add a -e option to specify the event name that
the flamegraph will be generated accordingly. If the -e option omitted,
the behavior remains unchanged.

Signed-off-by: Tianyou Li <tianyou.li@intel.com>
Reviewed-by: Pan Deng <pan.deng@intel.com>
Reviewed-by: Zhiguo Zhou <zhiguo.zhou@intel.com>
Reviewed-by: Wangyang Guo <wangyang.guo@intel.com>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
Link: https://lore.kernel.org/r/20250610040536.2390060-2-tianyou.li@intel.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/scripts/python/flamegraph.py

@@ -94,6 +94,11 @@ class FlameGraphCLI:
         return child
 
     def process_event(self, event):
+        # ignore events where the event name does not match
+        # the one specified by the user
+        if self.args.event_name and event.get("ev_name") != self.args.event_name:
+            return
+
         pid = event.get("sample", {}).get("pid", 0)
         # event["dso"] sometimes contains /usr/lib/debug/lib/modules/*/vmlinux
         # for user-space processes; let's use pid for kernel or user-space distinction
@@ -130,7 +135,10 @@ class FlameGraphCLI:
             else:
                 output = subprocess.check_output(["perf", "report", "--header-only"])
 
-            return output.decode("utf-8")
+            result = output.decode("utf-8")
+            if self.args.event_name:
+                result += "\nFocused event: " + self.args.event_name
+            return result
         except Exception as err:  # pylint: disable=broad-except
             print("Error reading report header: {}".format(err), file=sys.stderr)
             return ""
@@ -241,6 +249,11 @@ if __name__ == "__main__":
                         default=False,
                         action="store_true",
                         help="allow unprompted downloading of HTML template")
+    parser.add_argument("-e", "--event",
+                        default="",
+                        dest="event_name",
+                        type=str,
+                        help="specify the event to generate flamegraph for")
 
     cli_args = parser.parse_args()
     cli = FlameGraphCLI(cli_args)