perf flamegraph: Explicitly set utf-8 encoding

On some platforms the default encoding is not utf-8, which causes an
UnicodeDecodeError when reading the flamegraph template and writing the
flamegraph

Signed-off-by: Andreas Gerstmayr <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Michael Petlan <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/scripts/python/flamegraph.py

···
 from __future__ import print_function
 import sys
 import os
+import io
 import argparse
 import json
 
···
 
         if self.args.format == "html":
             try:
-                with open(self.args.template) as f:
+                with io.open(self.args.template, encoding="utf-8") as f:
                     output_str = f.read().replace("/** @flamegraph_json **/",
                                                   json_str)
             except IOError as e:
···
             output_fn = self.args.output or "stacks.json"
 
         if output_fn == "-":
-            sys.stdout.write(output_str)
+            with io.open(sys.stdout.fileno(), "w", encoding="utf-8", closefd=False) as out:
+                out.write(output_str)
         else:
             print("dumping data to {}".format(output_fn))
             try:
-                with open(output_fn, "w") as out:
+                with io.open(output_fn, "w", encoding="utf-8") as out:
                     out.write(output_str)
             except IOError as e:
                 print("Error writing output file: {}".format(e), file=sys.stderr)