Adding a SetRAILMode API.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index a58e66091d405f95a46fa00d722fe53e00dd6101..f5eb449d0d4eb7d213951704ff09ab8c1c708eb7 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -5357,6 +5357,29 @@ struct JitCodeEvent {
 };
 
 /**
+ * Option flags passed to the SetRAILMode function.

[ulan, 2016/05/20 11:15:56]

Link
https://developers.google.com/web/tools/chrome-devtools/profile/evaluate-perf...
?

+ */
+enum RAILMode {
+  // Default performance mode: V8 will optimize for both latency and
+  // throughput in this mode.
+  PERFORMANCE_DEFAULT,
+  // Response performance mode: In this mode moderate virtual machine latency
+  // is provided. V8 will try to avoid long JavaScript execution interruptions.
+  // Throughput may be throttled.
+  PERFORMANCE_RESPONSE,
+  // Animation performance mode: In this mode low virtual machine latency is

[Sami, 2016/05/20 11:08:03]

In my mind RESPONSE is the one where we'd want the absolute lowest latency and
ANIMATION is where we can tolerate the occasional missed frame. Are my wires
crossed?

In the scheduler we'd generally be in RESPONSE for very short durations.

[rmcilroy, 2016/05/20 11:12:52]

+1 - response would be for something where the animations are following user
input (e.g., scrolling) so latency would be super important, whereas animation
is where there are non-user-input related animations, where occasional dropped
frames and slight delay in doing the animation doesn't matter quite as much.

+  // provided. V8 will try to avoid as many JavaScript execution interruptions
+  // as possible. Throughput may be throttled
+  PERFORMANCE_ANIMATION,
+  // Idle performance mode: The embedder is idle. V8 can complete deferred work
+  // in this mode.
+  PERFORMANCE_IDLE,
+  // Load performance mode: In this mode high throughput is provided. V8 may
+  // turn off latency optimizations.
+  PERFORMANCE_LOAD
+};
+
+/**
  * Option flags passed to the SetJitCodeEventHandler function.
  */
 enum JitCodeEventOptions {
@@ -6158,6 +6181,13 @@ class V8_EXPORT Isolate {
   void IsolateInBackgroundNotification();
 
   /**
+   * Optional notification to tell V8 the current performance requirements
+   * of the embedder based on RAIL.
+   * V8 uses these notifications to guide heuristics.
+   */
+  void SetRAILMode(RAILMode rail_mode);
+
+  /**
    * Allows the host application to provide the address of a function that is
    * notified each time code is added, moved or removed.
    *