Force time elapsed queries on certain drivers.

ui/gl/gpu_timing.cc

Index: ui/gl/gpu_timing.cc
diff --git a/ui/gl/gpu_timing.cc b/ui/gl/gpu_timing.cc
index 45908c985188f56baaac43086cc62e9c01929248..c6e574ac578efcc96906398f92076d150a3a55ee 100644
--- a/ui/gl/gpu_timing.cc
+++ b/ui/gl/gpu_timing.cc
@@ -20,6 +20,12 @@ int64_t NanoToMicro(uint64_t nano_seconds) {
   return static_cast<int64_t>(up / base::Time::kNanosecondsPerMicrosecond);
 }
 
+int32_t QueryTimestampBits() {
+  GLint timestamp_bits;
+  glGetQueryiv(GL_TIMESTAMP, GL_QUERY_COUNTER_BITS, &timestamp_bits);
+  return static_cast<int32_t>(timestamp_bits);
+}
+
 class GPUTimingImpl : public GPUTiming {
  public:
    GPUTimingImpl(GLContextReal* context);
@@ -73,6 +79,7 @@ class GPUTimingImpl : public GPUTiming {
   int64_t offset_ = 0;  // offset cache when timer_type_ == kTimerTypeARB
   bool offset_valid_ = false;
   bool force_time_elapsed_query_ = false;
+  int32_t timestamp_bit_count_gl_ = -1;  // gl implementation timestamp bits
 
   uint32_t next_timer_query_id_ = 0;
   uint32_t next_good_timer_query_id_ = 0; // identify bad ids for disjoints.
@@ -318,6 +325,7 @@ GPUTimingImpl::GPUTimingImpl(GLContextReal* context) {
   } else if (context->HasExtension("GL_EXT_timer_query")) {
     timer_type_ = GPUTiming::kTimerTypeEXT;
     force_time_elapsed_query_ = true;
+    timestamp_bit_count_gl_ = 0;
   }
 }
 
@@ -392,6 +400,15 @@ void GPUTimingImpl::EndElapsedTimeQuery(scoped_refptr<QueryResult> result) {
 scoped_refptr<QueryResult> GPUTimingImpl::DoTimeStampQuery() {
   DCHECK(timer_type_ != GPUTiming::kTimerTypeInvalid);
 
+  // Certain GL drivers have timestamp bit count set to 0 which means timestamps
+  // aren't supported. Emulate them with time elapsed queries if that is the
+  // case.
+  if (timestamp_bit_count_gl_ == -1) {
+    DCHECK(timer_type_ != GPUTiming::kTimerTypeEXT);
+    timestamp_bit_count_gl_ = QueryTimestampBits();

[no sievers, 2016/02/17 23:08:45]

Do you have to do that every time though? Isn't GL_QUERY_COUNTER_BITS for
GL_TIMESTAMP more of a static property?

[David Yen, 2016/02/17 23:10:52]

It only lazily initializes it once. It's done lazily so contexts which do not
query timestamps do not have to query the counter.

[Ian Ewell, 2016/02/17 23:11:53]

It is only called once and then timestamp_bit_count_gl is updated so that it is
never called again. It is done here as it affects the fewest amount of tests
(putting it in the constructor broke twice as many tests before the fixes to the
tests.

+    force_time_elapsed_query_ = (timestamp_bit_count_gl_ == 0);
+  }
+
   if (force_time_elapsed_query_) {
     // Replace with elapsed timer queries instead.
     scoped_refptr<QueryResult> result = BeginElapsedTimeQuery();