add -h --help flag

tools/perfect.cpp

@@ -1,7 +1,9 @@
 #include <cassert>
 #include <cerrno>
+#include <chrono>
 #include <iostream>
 #include <string>
+#include <thread>
 #include <vector>
 
 #ifdef __linux__
@@ -155,6 +157,11 @@ int main(int argc, char **argv) {
   std::string stdoutPath;
   std::string stderrPath;
   int iters = 1;
+  int sleepMs = 1000;
+
+  bool help = false;
+
+  auto helpMode = option("-h", "--help").set(help).doc("show help");
 
   auto shieldGroup = ((option("-u").doc("number of unshielded CPUs") &
                        value("INT", numUnshielded)) |
@@ -184,8 +191,11 @@ int main(int argc, char **argv) {
                   (option("--stderr").doc("redirect child stderr") &
                    value("PATH", stderrPath)));
 
-  auto cli = ((noModMode | modMode),
+  auto cli =
-              (option("-n").doc("run multiple times") & value("INT", iters)),
+      helpMode |
+      ((noModMode | modMode),
+       (option("--sleep-ms").doc("sleep before run") & value("INT", sleepMs)),
+       (option("-n").doc("run multiple times") & value("INT", iters)), helpMode,
        // run everything after "--"
        required("--") & greedy(values("cmd", program))
 
@@ -197,6 +207,12 @@ int main(int argc, char **argv) {
     return -1;
   }
 
+  if (help) {
+    auto fmt = doc_formatting{}.doc_column(31);
+    std::cout << make_man_page(cli, argv[0], fmt);
+    return 0;
+  }
+
   // open the redirect files, if needed
   int errf = 0;
   int outf = 0;
@@ -333,6 +349,12 @@ int main(int argc, char **argv) {
       PERFECT(perfect::drop_caches());
     }
 
+    // sleep before each run
+    if (sleepMs) {
+      std::cerr << "sleep " << sleepMs << " ms before run\n";
+      std::this_thread::sleep_for(std::chrono::milliseconds(sleepMs));
+    }
+
     std::cerr << "exec ";
     for (size_t i = 0; i < args.size() - 1; ++i) {
       std::cerr << args[i] << " ";