benchmark: Add http-flamegraph

This is very similar to http.sh, but generates a flamegraph
with dtrace, pruning off the single-hit stacks so that we can
more easily see the places where relevant amounts of time are
spent.

benchmark/http-flamegraph.sh

@@ -0,0 +1,79 @@
+#!/bin/bash
+cd "$(dirname "$(dirname $0)")"
+if type sysctl &>/dev/null; then
+  sudo sysctl -w net.inet.ip.portrange.first=12000
+  sudo sysctl -w net.inet.tcp.msl=1000
+  sudo sysctl -w kern.maxfiles=1000000 kern.maxfilesperproc=1000000
+fi
+ulimit -n 100000
+
+./node benchmark/http_simple.js &
+nodepid=$!
+echo "node pid = $nodepid"
+sleep 1
+
+# has to stay alive until dtrace exits
+dtrace -n 'profile-97/pid == '$nodepid' && arg1/{ @[jstack(150, 8000)] = count(); } tick-60s { exit(0); }' > stacks.src &
+dtracepid=$!
+echo "dtrace pid = $dtracepid"
+
+test () {
+  n=$1
+  c=$2
+  k=$3
+  ab $k -n $n -c $c http://127.0.0.1:8000/${TYPE:-bytes}/${LENGTH:-1024} \
+    2>&1 | grep Req
+}
+
+test 10000 100
+test 10000 10 -k
+test 10000 100 -k
+test 30000 100 -k
+test 60000 100 -k
+
+echo 'Keep going until dtrace stops listening...'
+while pargs $dtracepid &>/dev/null; do
+  ab -k -n 60000 -c 100 http://127.0.0.1:8000/${TYPE:-bytes}/${LENGTH:-1024} 2>&1 | grep Req
+done
+
+kill $nodepid
+
+echo 'Pluck off all the stacks that only happen once.'
+
+node -e '
+var fs = require("fs");
+var data = fs.readFileSync("stacks.src", "utf8").split(/\n/);
+var out = fs.createWriteStream("stacks.out");
+function write(l) {
+  out.write(l + "\n");
+}
+write(data[0]);
+write(data[1]);
+write(data[2]);
+
+var stack = [];
+var i = 4;
+var saw2 = false
+for (; i < data.length && !saw2; i++) {
+  if (data[i] === "                2") {
+    stack.forEach(function(line) {
+      write(line);
+    });
+    write(data[i]);
+    saw2 = true;
+  } else if (data[i] === "                1") {
+    stack = [];
+  } else {
+    stack.push(data[i]);
+  }
+}
+
+for (; i < data.length; i++)
+  write(data[i]);
+'
+
+echo 'Turn the stacks into a svg'
+stackvis dtrace flamegraph-svg < stacks.out > stacks.svg
+
+echo ''
+echo 'done. Results in stacks.svg'