Add Linux perf profiling wrapper script.

tools/run-perf.sh

Index: tools/run-perf.sh
diff --git a/tools/run-perf.sh b/tools/run-perf.sh
new file mode 100755
index 0000000000000000000000000000000000000000..bbda0ae00c6219bcdfc07327db43ae35237411da
--- /dev/null
+++ b/tools/run-perf.sh
@@ -0,0 +1,52 @@
+#! /bin/bash

[Stefano Sanfilippo, 2016/03/09 18:23:55]

bash and not sh because of the == between strings below. Should we fix this
bashism?

+#
+# Copyright 2016 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+#
+
+########## Global variable definitions
+
+# Ensure that <your CPU clock> / $SAMPLE_EVERY_N_CYCLES < $MAXIMUM_SAMPLE_RATE.
+MAXIMUM_SAMPLE_RATE=10000000
+SAMPLE_EVERY_N_CYCLES=10000
+SAMPLE_RATE_CONFIG_FILE="/proc/sys/kernel/perf_event_max_sample_rate"
+KERNEL_MAP_CONFIG_FILE="/proc/sys/kernel/kptr_restrict"
+CALL_GRAPH_METHOD="fp"  # dwarf does not play nice with JITted objects.
+
+########## Usage
+
+usage() {
+cat << EOF
+usage: $0 <benchmark_command>
+
+Executes <benchmark_command> under observation by Linux perf.
+Sampling event is cycles in user space, call graphs are recorded.
+EOF
+}
+
+if [ $# -eq 0 ] || [ "$1" == "-h" ]  || [ "$1" == "--help" ] ; then
+  usage
+  exit 1
+fi
+
+########## Actual script execution
+
+ACTUAL_SAMPLE_RATE=$(cat $SAMPLE_RATE_CONFIG_FILE)
+if [ "$ACTUAL_SAMPLE_RATE" -lt "$MAXIMUM_SAMPLE_RATE" ] ; then
+  echo "Setting appropriate maximum sample rate..."
+  echo $MAXIMUM_SAMPLE_RATE | sudo tee $SAMPLE_RATE_CONFIG_FILE
+fi
+
+ACTUAL_KERNEL_MAP_RESTRICTION=$(cat $KERNEL_MAP_CONFIG_FILE)
+if [ "$ACTUAL_KERNEL_MAP_RESTRICTION" -ne "0" ] ; then
+  echo "Disabling kernel address map restriction..."
+  echo 0 | sudo tee $KERNEL_MAP_CONFIG_FILE
+fi
+
+echo "Running benchmark..."
+perf record -R \
+  -e cycles:u \
+  -c $SAMPLE_EVERY_N_CYCLES \
+  --call-graph $CALL_GRAPH_METHOD \
+  -i $@ --perf_basic_prof