Help eglSwapBuffers() procedure in triple buffering

Dear All,

I confused about eglSwapBuffers() function on ARM MALI400

First, Here is development environment.

Target Chip: A53+Mali400MP2 chip

Target Board OS: Linux OS 32 Bit

Mali Drivers: r6p1-01rel0

Target Application: OpenGLES2.0,  fbdev based Triple Buffering

Host OS: Fedora fc20.x86_64bit

Here is my main rendering loop.

The loop receives renderFrameEvent messages sent from another thread that contain a list of OpenGL commands to execute.

All of the OpenGL drawing calls are executed in the renderFrameEvent->commandList->flush() call.

while ((message = thread->msgPort.waitPort())) {
        printf("Message Loop message=%s,pending=%d\n", message->getClass().c_str(), thread->msgPort.countPending());

        if (message->getClass() == "RenderOpenGLFrameEvent") {
            std::chrono::time_point<std::chrono::high_resolution_clock> startTime, renderTime, endTime;

// Start Timing
            startTime = std::chrono::high_resolution_clock::now();

           renderFrameEvent = std::static_pointer_cast<RenderOpenGLFrameEvent> (message);

// Draw
            renderFrameEvent->commandList->flush();

            eglSwapBuffers(egl_display, egl_surface);

// End Timing
            renderTime = std::chrono::high_resolution_clock::now();

            std::chrono::duration<double> renderDuration = renderTime - startTime;

            printf("renderDuration=%f\n",renderDuration.count());
        }
    }

This is the output when you press a button to scroll:

Message Loop message=RenderOpenGLFrameEvent,pending=0

renderDuration=0.000656

Message Loop message=RenderOpenGLFrameEvent,pending=0

renderDuration=0.000631

Message Loop message=RenderOpenGLFrameEvent,pending=0

renderDuration=0.000601

Message Loop message=RenderOpenGLFrameEvent,pending=0

renderDuration=0.000619

Message Loop message=RenderOpenGLFrameEvent,pending=0

renderDuration=0.009073

Message Loop message=RenderOpenGLFrameEvent,pending=1

renderDuration=0.016451

Message Loop message=RenderOpenGLFrameEvent,pending=2

renderDuration=0.016368

Message Loop message=RenderOpenGLFrameEvent,pending=2

renderDuration=0.016457

So there are no frames pending at the start of this log, so two back buffers should be available. eglSwapBuffers() is then called 6 times.

With triple buffering, eglSwapBuffers() should probably not wait for the vertical sync for the first two frames, otherwise it can't pipeline the operation.

I don't know why 4 frames return immediately in this case though, what do I need to do to accurately measure the frame rate?

Thanks!