4 files changed, 20 insertions, 30 deletions

diff --git a/bench/nanobench.cpp b/bench/nanobench.cpp
index 4453707416..a9862c6ef0 100644
--- a/bench/nanobench.cpp
+++ b/bench/nanobench.cpp
@@ -50,8 +50,6 @@ 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) {
@@ -95,13 +93,8 @@ static double estimate_timer_overhead() {
 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.
@@ -288,6 +281,8 @@ int tool_main(int argc, char** argv) {
     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) {
diff --git a/tools/Stats.h b/tools/Stats.h
index 4fddc9bc18..8487a9497d 100644
--- a/tools/Stats.h
+++ b/tools/Stats.h
@@ -1,8 +1,6 @@
 #ifndef Stats_DEFINED
 #define Stats_DEFINED
 
-#include <math.h>
-
 #include "SkString.h"
 #include "SkTSort.h"
 
@@ -50,7 +48,7 @@ struct Stats {
             s -= min;
             s /= (max - min);
             s *= (SK_ARRAY_COUNT(kBars) - 1);
-            const size_t bar = (size_t)round(s);
+            const size_t bar = (size_t)(s + 0.5);
             SK_ALWAYSBREAK(bar < SK_ARRAY_COUNT(kBars));
             plot.append(kBars[bar]);
         }
diff --git a/tools/timer/SysTimer_windows.cpp b/tools/timer/SysTimer_windows.cpp
index 2f9d0a5d58..8e45b4a68e 100644
--- a/tools/timer/SysTimer_windows.cpp
+++ b/tools/timer/SysTimer_windows.cpp
@@ -6,6 +6,8 @@
  */
 #include "SysTimer_windows.h"
 
+#include <intrin.h>
+
 static ULONGLONG win_cpu_time() {
     FILETIME createTime;
     FILETIME exitTime;
@@ -23,11 +25,6 @@ static ULONGLONG win_cpu_time() {
     return start_cpu_sys.QuadPart + start_cpu_usr.QuadPart;
 }
 
-void SysTimer::startWall() {
-    if (0 == ::QueryPerformanceCounter(&fStartWall)) {
-        fStartWall.QuadPart = 0;
-    }
-}
 void SysTimer::startCpu() {
     fStartCpu = win_cpu_time();
 }
@@ -36,21 +33,21 @@ double SysTimer::endCpu() {
     ULONGLONG end_cpu = win_cpu_time();
     return static_cast<double>(end_cpu - fStartCpu) / 10000.0L;
 }
+
+// On recent Intel chips (roughly, "has Core or Atom in its name") __rdtsc will always tick
+// at the CPU's maximum rate, even while power management clocks the CPU up and down.
+// That's great, because it makes measuring wall time super simple.
+
+void SysTimer::startWall() {
+    fStartWall = __rdtsc();
+}
+
 double SysTimer::endWall() {
-    LARGE_INTEGER end_wall;
-    if (0 == ::QueryPerformanceCounter(&end_wall)) {
-        end_wall.QuadPart = 0;
-    }
+    unsigned __int64 end = __rdtsc();
 
-    LARGE_INTEGER ticks_elapsed;
-    ticks_elapsed.QuadPart = end_wall.QuadPart - fStartWall.QuadPart;
+    // This seems to, weirdly, give the CPU frequency in kHz.  That's exactly what we want!
+    LARGE_INTEGER freq_khz;
+    QueryPerformanceFrequency(&freq_khz);
 
-    LARGE_INTEGER frequency;
-    if (0 == ::QueryPerformanceFrequency(&frequency)) {
-        return 0.0L;
-    } else {
-        return static_cast<double>(ticks_elapsed.QuadPart)
-             / static_cast<double>(frequency.QuadPart)
-             * 1000.0L;
-    }
+    return static_cast<double>(end - fStartWall) / static_cast<double>(freq_khz.QuadPart);
 }
diff --git a/tools/timer/SysTimer_windows.h b/tools/timer/SysTimer_windows.h
index 62a9445134..380debd313 100644
--- a/tools/timer/SysTimer_windows.h
+++ b/tools/timer/SysTimer_windows.h
@@ -19,7 +19,7 @@ public:
     double endWall();
 private:
     ULONGLONG fStartCpu;
-    LARGE_INTEGER fStartWall;
+    unsigned __int64 fStartWall;
 };
 
 #endif