CC serialization perftests: more accurate "num runs in 2 seconds".

cc/ipc/cc_serialization_perftest.cc

Index: cc/ipc/cc_serialization_perftest.cc
diff --git a/cc/ipc/cc_serialization_perftest.cc b/cc/ipc/cc_serialization_perftest.cc
index 30d7835a1cc4198be9a3c84717abdece2f27a150..b91cd853a3e431db89b6991d2d0e931642a07d4a 100644
--- a/cc/ipc/cc_serialization_perftest.cc
+++ b/cc/ipc/cc_serialization_perftest.cc
@@ -60,7 +60,9 @@ class CCSerializationPerfTest : public testing::Test {
     size_t count = 0;
     while (start < end) {
       for (int i = 0; i < kTimeCheckInterval; ++i) {
-        ++count;
+        base::TimeTicks now = base::TimeTicks::Now();
+        if (now < end)
+          ++count;
         CompositorFrame compositor_frame;
         ReadMessage(&msg, &compositor_frame);
       }
@@ -93,9 +95,11 @@ class CCSerializationPerfTest : public testing::Test {
     size_t count = 0;
     while (start < end) {
       for (int i = 0; i < kTimeCheckInterval; ++i) {
+        base::TimeTicks now = base::TimeTicks::Now();
+        if (now < end)
+          ++count;
         IPC::Message msg(1, 2, IPC::Message::PRIORITY_NORMAL);
         IPC::ParamTraits<CompositorFrame>::Write(&msg, frame);
-        ++count;
       }
 
       base::TimeTicks now = base::TimeTicks::Now();
@@ -128,9 +132,11 @@ class CCSerializationPerfTest : public testing::Test {
     size_t count = 0;
     while (start < end) {
       for (int i = 0; i < kTimeCheckInterval; ++i) {

[danakj, 2016/07/29 22:04:56]

Just decrease kTimeCheckInterval for those tests and maybe EXPECT that it's
larger than some function of the number the test reports?

[yzshen1, 2016/07/29 22:12:12]

Decreasing the number of kTimeCheckInterval may affect the min_frame_*_time,
because that is an average of kTimeCheckInterval runs.

Is it a concern that we may invoke base::TimeTicks::Now() too many times? I
compared the numbers before/after the change, it seems the difference is
negligible.

WDYT? Thanks!

[danakj, 2016/07/29 22:14:02]

Ah ok.

+        base::TimeTicks now = base::TimeTicks::Now();
+        if (now < end)
+          ++count;

[danakj, 2016/07/29 22:14:02]

Can you do this at the bottom of the loop. And you should be able to reuse this
Now() value below the loop if you scope the variable right.

[yzshen1, 2016/07/31 06:57:17]

Done.

         CompositorFrame compositor_frame;
         mojom::CompositorFrame::Deserialize(data, &compositor_frame);
-        ++count;
       }
 
       base::TimeTicks now = base::TimeTicks::Now();
@@ -162,9 +168,11 @@ class CCSerializationPerfTest : public testing::Test {
     size_t count = 0;
     while (start < end) {
       for (int i = 0; i < kTimeCheckInterval; ++i) {
+        base::TimeTicks now = base::TimeTicks::Now();
+        if (now < end)
+          ++count;
         mojo::Array<uint8_t> data = mojom::CompositorFrame::Serialize(&frame);
         DCHECK_GT(data.size(), 0u);
-        ++count;
       }
 
       base::TimeTicks now = base::TimeTicks::Now();