Add samplingTime mode to nanobench

tools/timer/SysTimer_posix.cpp

Index: tools/timer/SysTimer_posix.cpp
diff --git a/tools/timer/SysTimer_posix.cpp b/tools/timer/SysTimer_posix.cpp
index 4b7d708aab0c4a7e899da8c55ddb409f43845a16..1f05ca9c38aee47899f96b3c16e19aa8e6ccf1d8 100644
--- a/tools/timer/SysTimer_posix.cpp
+++ b/tools/timer/SysTimer_posix.cpp
@@ -49,3 +49,21 @@ double SysTimer::endWall() {
     }
     return interval_in_ms(fWall, end_wall);
 }
+
+static timespec init_launch_time() {
+    timespec launchTime;
+    if (-1 == clock_gettime(CLOCK_MONOTONIC, &launchTime)) {
+        timespec none = {0, 0};
+        return none;
+    }
+    return launchTime;
+};
+
+double GetTimeMs() {
+    static const timespec launchTime = init_launch_time();
+    timespec now;
+    if (-1 == clock_gettime(CLOCK_MONOTONIC, &now)) {
+        return 0;
+    }
+    return interval_in_ms(launchTime, now);
+}