Use __rdtsc on Windows.

bench/nanobench.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include <ctype.h>
 
 #include "Benchmark.h"
@@ skipping 32 matching lines @@
 DEFINE_string(config, "nonrendering 8888 gpu", "Configs to measure. Options: "
               "565 8888 gpu nonrendering debug nullgpu msaa4 msaa16 nvprmsaa4 nvprmsaa16 angle");
 DEFINE_double(gpuMs, 5, "Target bench time in millseconds for GPU.");
 DEFINE_int32(gpuFrameLag, 5, "Overestimate of maximum number of frames GPU allows to lag.");
 
 DEFINE_bool(cpu, true, "Master switch for CPU-bound work.");
 DEFINE_bool(gpu, true, "Master switch for GPU-bound work.");
 
 DEFINE_string(outResultsFile, "", "If given, write results here as JSON.");
 DEFINE_bool(resetGpuContext, true, "Reset the GrContext before running each bench.");
-DEFINE_int32(maxCalibrationAttempts, 3,
-             "Try up to this many times to guess loops for a bench, or skip the bench.");
 
 
 static SkString humanize(double ms) {
     if (ms > 1e+3) return SkStringPrintf("%.3gs",  ms/1e3);
     if (ms < 1e-3) return SkStringPrintf("%.3gns", ms*1e6);
 #ifdef SK_BUILD_FOR_WIN
     if (ms < 1)    return SkStringPrintf("%.3gus", ms*1e3);
 #else
     if (ms < 1)    return SkStringPrintf("%.3gµs", ms*1e3);
 #endif
@@ skipping 23 matching lines @@
     double overhead = 0;
     for (int i = 0; i < FLAGS_overheadLoops; i++) {
         overhead += time(1, NULL, NULL, NULL);
     }
     return overhead / FLAGS_overheadLoops;
 }
 
 static int cpu_bench(const double overhead, Benchmark* bench, SkCanvas* canvas, double* samples) {
     // First figure out approximately how many loops of bench it takes to make overhead negligible.
     double bench_plus_overhead;
-    int round = 0;
     do {
         bench_plus_overhead = time(1, bench, canvas, NULL);
-        if (++round == FLAGS_maxCalibrationAttempts) {
-            // At some point we have to just give up.
-            return 0;
-        }
     } while (bench_plus_overhead < overhead);
 
     // Later we'll just start and stop the timer once but loop N times.
     // We'll pick N to make timer overhead negligible:
     //
     //          overhead
     //  -------------------------  < FLAGS_overheadGoal
     //  overhead + N * Bench Time
     //
     // where bench_plus_overhead ≈ overhead + Bench Time.
@@ skipping 166 matching lines @@
     MultiResultsWriter log;
     SkAutoTDelete<JSONResultsWriter> json;
     if (!FLAGS_outResultsFile.isEmpty()) {
         json.reset(SkNEW(JSONResultsWriter(FLAGS_outResultsFile[0])));
         log.add(json.get());
     }
     CallEnd<MultiResultsWriter> ender(log);
     fill_static_options(&log);
 
     const double overhead = estimate_timer_overhead();
+    SkDebugf("Timer overhead: %s\n", humanize(overhead).c_str());
+
     SkAutoTMalloc<double> samples(FLAGS_samples);
 
     if (FLAGS_runOnce) {
         SkDebugf("--runOnce is true; times would only be misleading so we won't print them.\n");
     } else if (FLAGS_verbose) {
         // No header.
     } else if (FLAGS_quiet) {
         SkDebugf("median\tbench\tconfig\n");
     } else {
         SkDebugf("loops\tmin\tmedian\tmean\tmax\tstddev\tsamples\tconfig\tbench\n");
@@ skipping 76 matching lines @@
     }
 
     return 0;
 }
 
 #if !defined SK_BUILD_FOR_IOS
 int main(int argc, char * const argv[]) {
     return tool_main(argc, (char**) argv);
 }
 #endif