perf script: Add -e option to flamegraph script

JIRA: https://issues.redhat.com/browse/RHEL-78200

upstream
========
commit 9a79c50
Author: Tianyou Li <tianyou.li@intel.com>
Date: Tue Jun 10 12:04:23 2025 +0800

description
===========
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>

Signed-off-by: Anubhav Shelat <ashelat@redhat.com>

Author: AnubhavS1

tools/perf/scripts/python/flamegraph.py

@@ -94,6 +94,11 @@ def find_or_create_node(node, name, libtype):
         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 @@ def get_report_header(self):
             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 @@ def trace_end(self):
                         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)