As part of a transaction, and therefor as part of a composition, we generally submit a certain amount of visual data to the compositor that was generated at certain points in the past. By being able to associate this contents and the time it was generated with a composition we'd be able to fairly accurately determine the total latency from generation of the event (for example user input), to the result being shown on the screen (i.e. max one frame after composition takes place). I've discussed this with Markus and I have some ideas on an infrastructure to do this.

Comment on attachment 9019504 [details] [diff] [review] Part 1: Add the ability to register CompositionPayloads and forward through transactions v3 Review of attachment 9019504 [details] [diff] [review]: ----------------------------------------------------------------- The approach looks good to me. ::: gfx/layers/Layers.h @@ +730,5 @@ > > virtual CompositorBridgeChild* GetCompositorBridgeChild() { return nullptr; } > > + void RegisterPayload(const CompositionPayload& aPayload) { mPayload.AppendElement(aPayload); MOZ_ASSERT(mPayload.Length() < 10000); } > + void RegisterPayload(const InfallibleTArray<CompositionPayload>& aPayload) { mPayload.AppendElements(aPayload); MOZ_ASSERT(mPayload.Length() < 10000); } some long lines here ::: gfx/layers/LayersTypes.h @@ +472,5 @@ > + bool operator ==(const CompositionPayload& aOther) const { > + return mType == aOther.mType && mTimeStamp == aOther.mTimeStamp; > + } > + /* The type of payload that is in this composition */ > + CompositionPayloadType mType; end-of-line whitespace ::: gfx/layers/ipc/LayersMessageUtils.h @@ +666,5 @@ > {}; > > +template <> > +struct ParamTraits<mozilla::layers::CompositionPayload> > + : public PlainOldDataSerializer<mozilla::layers::CompositionPayload> Let's actually handwrite the serialization for this. That'll give us protection against invalid enum values from compromised content processes, too, and it would make me feel better about correct TimeStamp serialization.

Carrying r+.

Carrying r+.

WR will need some sort of equivelant of this.

This works, although perhaps something more specialized is desirable here where the payload is stored with the Composite trace marker and displayed in the profiler sidebar, I'll let you decide what you want to do here Markus, if you provide me with pointers I can implement something better.

Pushed by bschouten@mozilla.com: https://hg.mozilla.org/integration/mozilla-inbound/rev/4c1fade7ceeb Part 1: Add CompositionPayload type and allow submitting it as part of a transaction. r=mstange https://hg.mozilla.org/integration/mozilla-inbound/rev/76070b4feec3 Part 2: Propagate composition payload from clients to host. r=rhunt https://hg.mozilla.org/integration/mozilla-inbound/rev/a123204b6b0d Part 3: Add profiler markers for payload presentarion. r=mstange