[PATCH] Minor improvements for perf script flamegraph

[Tianyou Li]

When processing the perf data file generated with multiple events,
the flamegraph script will count all the events regardless of
different event names. If specify the perf data file with -i option,
the script will try to read the header information regardless of
the file name specified, instead it will try to access the perf.data.

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. If the -i option specified, the header
information will be read from that file.

Signed-off-by: Tianyou Li <tianyou.li@xxxxxxxxx>
Reviewed-by: Pan Deng <pan.deng@xxxxxxxxx>
Reviewed-by: Zhiguo Zhou <zhiguo.zhou@xxxxxxxxx>
Reviewed-by: Wangyang Guo <wangyang.guo@xxxxxxxxx>
Reviewed-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
---
 tools/perf/scripts/python/flamegraph.py | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/tools/perf/scripts/python/flamegraph.py b/tools/perf/scripts/python/flamegraph.py
index cf7ce8229a..eb78b93925 100755
--- a/tools/perf/scripts/python/flamegraph.py
+++ b/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
@@ -123,8 +128,15 @@ class FlameGraphCLI:
             return ""
 
         try:
-            output = subprocess.check_output(["perf", "report", "--header-only"])
-            return output.decode("utf-8")
+            if self.args.input:
+                output = subprocess.check_output(["perf", "script", "--header-only", "-i", self.args.input])
+            else:
+                output = subprocess.check_output(["perf", "report", "--header-only"])
+
+            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 ""
@@ -235,6 +247,11 @@ 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)
-- 
2.43.5