Improve base::RandBytes() performance by 1.75x-2.10x on POSIX.

base/rand_util_unittest.cc

Index: base/rand_util_unittest.cc
diff --git a/base/rand_util_unittest.cc b/base/rand_util_unittest.cc
index e0e85ecaa91a6d38e63e57397e80a42848a3cdc5..81281dba9336f44aa1d30fb5958000745d681385 100644
--- a/base/rand_util_unittest.cc
+++ b/base/rand_util_unittest.cc
@@ -7,6 +7,9 @@
 #include <algorithm>
 #include <limits>
 
+#include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/time/time.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
@@ -120,3 +123,19 @@ TEST(RandUtilTest, RandUint64ProducesBothValuesOfAllBits) {
 
   FAIL() << "Didn't achieve all bit values in maximum number of tries.";
 }
+
+TEST(RandUtilTest, DISABLED_RandBytesPerf) {

[wtc, 2014/01/22 22:29:09]

We should document why this test is DISABLED.

[DaleCurtis, 2014/01/22 22:54:14]

Done.

+  // Benchmark the performance of |kTestIterations| of RandBytes() using a
+  // buffer size of |kTestBufferSize|.
+  const int kTestIterations = 10;
+  const size_t kTestBufferSize = 1 * 1024 * 1024;
+
+  scoped_ptr<uint8[]> buffer(new uint8[kTestBufferSize]);
+  const base::TimeTicks now = base::TimeTicks::HighResNow();
+  for (int i = 0; i < kTestIterations; ++i)
+    base::RandBytes(buffer.get(), kTestBufferSize);
+  const base::TimeTicks end = base::TimeTicks::HighResNow();
+
+  LOG(INFO) << "RandBytes(" << kTestBufferSize << ") took: "
+            << (end - now).InMicroseconds() << "µs";
+}