Add nanobench, a fresh look at our microbenchmark harness.

bench/nanobench.cpp

Index: bench/nanobench.cpp
diff --git a/bench/nanobench.cpp b/bench/nanobench.cpp
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+/*
+ * 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 "Benchmark.h"
+#include "CrashHandler.h"
+#include "Stats.h"
+#include "Timer.h"
+
+#include "SkCanvas.h"
+#include "SkCommandLineFlags.h"
+#include "SkForceLinking.h"
+#include "SkGraphics.h"
+#include "SkString.h"
+#include "SkSurface.h"
+
+__SK_FORCE_IMAGE_DECODER_LINKING;
+
+DEFINE_int32(samples, 10, "Number of samples to measure for each bench.");
+DEFINE_int32(overheadLoops, 100000, "Loops to estimate timer overhead.");
+DEFINE_double(overheadGoal, 0.0001,
+              "Loop until timer overhead is at most this fraction of our measurments.");
+DEFINE_string(match, "", "The usual filters on file names of benchmarks to measure.");
+DEFINE_bool2(quiet, q, false, "Print only bench name and minimum sample.");
+DEFINE_bool2(verbose, v, false, "Print all samples.");
+DEFINE_string(config, "8888 nonrendering",
+              "Configs to measure. Options: 565 8888 nonrendering");
+
+// TODO: GPU benches
+
+static SkString humanize(double ms) {
+    if (ms > 1e+3) return SkStringPrintf("%.3gs",  ms/1e3);
+    if (ms < 1e-3) return SkStringPrintf("%.3gns", ms*1e6);
+    if (ms < 1)    return SkStringPrintf("%.3gµs", ms*1e3);
+    return SkStringPrintf("%.3gms", ms);
+}
+
+static double estimate_timer_overhead() {
+    double overhead = 0;
+    WallTimer timer;
+    for (int i = 0; i < FLAGS_overheadLoops; i++) {
+        timer.start();
+        timer.end();
+        overhead += timer.fWall;
+    }
+    return overhead / FLAGS_overheadLoops;
+}
+
+static void safe_flush(SkCanvas* canvas) {
+    if (canvas) {
+        canvas->flush();
+    }
+}
+
+static int guess_loops(double overhead, Benchmark* bench, SkCanvas* canvas) {
+    WallTimer timer;
+
+    // Measure timer overhead and bench time together.
+    do {
+        timer.start();
+        bench->draw(1, canvas);
+        safe_flush(canvas);
+        timer.end();
+    } while (timer.fWall < overhead);  // Shouldn't normally happen.
+
+    // Later we'll just start and stop the timer once, but loop N times.
+    // We'll pick N to make timer overhead negligible:
+    //
+    //           Timer Overhead
+    //  -------------------------------  < FLAGS_overheadGoal
+    //  Timer Overhead + N * Bench Time
+    //
+    // where timer.fWall ≈ Timer Overhead + Bench Time.
+    //
+    // Doing some math, we get:
+    //
+    //  (Timer Overhead / FLAGS_overheadGoal) - Timer Overhead
+    //  -----------------------------------------------------  < N
+    //           (timer.fWall - Timer Overhead)
+    //
+    // Luckily, this also works well in practice. :)
+    const double numer = overhead / FLAGS_overheadGoal - overhead;
+    const double denom = timer.fWall - overhead;
+    return (int)ceil(numer / denom);
+}
+
+static bool push_config_if_enabled(const char* config, SkTDArray<const char*>* configs) {
+    if (FLAGS_config.contains(config)) {
+        configs->push(config);
+        return true;
+    }
+    return false;
+}
+
+static void create_surfaces(Benchmark* bench,
+                            SkTDArray<SkSurface*>* surfaces,
+                            SkTDArray<const char*>* configs) {
+
+    if (bench->isSuitableFor(Benchmark::kNonRendering_Backend)
+        && push_config_if_enabled("nonrendering", configs)) {
+        surfaces->push(NULL);
+    }
+
+    if (bench->isSuitableFor(Benchmark::kRaster_Backend)) {
+        const int w = bench->getSize().fX,
+                  h = bench->getSize().fY;
+
+        if (push_config_if_enabled("8888", configs)) {
+            const SkImageInfo info = { w, h, kN32_SkColorType, kPremul_SkAlphaType };
+            surfaces->push(SkSurface::NewRaster(info));
+        }
+
+        if (push_config_if_enabled("565", configs)) {
+            const SkImageInfo info = { w, h, kRGB_565_SkColorType, kOpaque_SkAlphaType };
+            surfaces->push(SkSurface::NewRaster(info));
+        }
+    }
+}
+
+int tool_main(int argc, char** argv);
+int tool_main(int argc, char** argv) {
+    SetupCrashHandler();
+    SkAutoGraphics ag;
+    SkCommandLineFlags::Parse(argc, argv);
+
+    const double overhead = estimate_timer_overhead();
+
+    if (FLAGS_verbose) {
+        // No header.
+    } else if (FLAGS_quiet) {
+        SkDebugf("min\tbench\tconfig\n");
+    } else {
+        SkDebugf("loops\tmin\tmean\tmax\tstddev\tbench\tconfig\n");
+    }
+
+    for (const BenchRegistry* r = BenchRegistry::Head(); r != NULL; r = r->next()) {
+        SkAutoTDelete<Benchmark> bench(r->factory()(NULL));
+        if (SkCommandLineFlags::ShouldSkip(FLAGS_match, bench->getName())) {
+            continue;
+        }
+
+        SkTDArray<SkSurface*> surfaces;
+        SkTDArray<const char*> configs;
+        create_surfaces(bench.get(), &surfaces, &configs);
+
+        bench->preDraw();
+        for (int j = 0; j < surfaces.count(); j++) {
+            SkCanvas* canvas = surfaces[j] ? surfaces[j]->getCanvas() : NULL;
+            const char* config = configs[j];
+
+            bench->draw(1, canvas);  // Just paranoid warmup.
+            safe_flush(canvas);
+            const int loops = guess_loops(overhead, bench.get(), canvas);
+
+            SkAutoTMalloc<double> samples(FLAGS_samples);
+            WallTimer timer;
+            for (int i = 0; i < FLAGS_samples; i++) {
+                timer.start();
+                bench->draw(loops, canvas);
+                safe_flush(canvas);
+                timer.end();
+                samples[i] = timer.fWall / loops;
+            }
+
+            Stats stats(samples.get(), FLAGS_samples);
+
+            if (FLAGS_verbose) {
+                for (int i = 0; i < FLAGS_samples; i++) {
+                    SkDebugf("%s  ", humanize(samples[i]).c_str());
+                }
+                SkDebugf("%s\n", bench->getName());
+            } else if (FLAGS_quiet) {
+                if (configs.count() == 1) {
+                    config = ""; // Only print the config if we run the same bench on more than one.
+                }
+                SkDebugf("%s\t%s\t%s\n", humanize(stats.min).c_str(), bench->getName(), config);
+            } else {
+                const double stddev_percent = 100 * sqrt(stats.var) / stats.mean;
+                SkDebugf("%d\t%s\t%s\t%s\t%.0f%%\t%s\t%s\n"
+                        , loops
+                        , humanize(stats.min).c_str()
+                        , humanize(stats.mean).c_str()
+                        , humanize(stats.max).c_str()
+                        , stddev_percent
+                        , bench->getName()
+                        , config
+                        );
+            }
+        }
+        surfaces.deleteAll();
+    }
+
+    return 0;
+}
+
+#if !defined SK_BUILD_FOR_IOS
+int main(int argc, char * const argv[]) {
+    return tool_main(argc, (char**) argv);
+}
+#endif