Update NCCL tests

src/timer.cc

@@ -0,0 +1,28 @@
+#include "timer.h"
+
+// Make sure to compile this translation unit with the host compiler and not
+// nvcc, lest you hit an internal compiler error (ICE) with GCC 10.3.0
+#include <chrono>
+
+namespace {
+  std::uint64_t now() {
+    using clock = std::chrono::steady_clock;
+    return std::chrono::duration_cast<std::chrono::nanoseconds>(clock::now().time_since_epoch()).count();
+  }
+}
+
+timer::timer() {
+  t0 = now();
+}
+
+double timer::elapsed() const {
+  std::uint64_t t1 = now();
+  return 1.e-9*(t1 - t0);
+}
+
+double timer::reset() {
+  std::uint64_t t1 = now();
+  double ans = 1.e-9*(t1 - t0);
+  t0 = t1;
+  return ans;
+}