This document discusses techniques for measuring and improving mobile app performance to achieve 60 frames per second (FPS). It explains that the UI thread is responsible for Vsync, input, animation, and drawing each frame. Measuring FPS accurately requires using the Choreographer class to detect dropped or delayed frames. The document also presents approaches like AutoBlame and AutoProfiler used by Facebook to identify sources of jank or stutter. It recommends using Systrace with custom markers on a Nexus 4 running KitKat to quickly profile problem areas and improve performance.

1. The Road to 60 FPS
Jason Sendros

2. Why care?

3. Android Frame Rendering Deep Dive

4. What happens on the UI thread?
VSync
Input
Animation
Draw
Frame 1 Frame 2 Frame 3
Get used to this guy

5. 60FPS is inaccurate
Galaxy Core 2
33fps
Nexus 5
60fps
55fps
Nexus 4
60fps
49fps

6. How do you measure a skipped frame?

7. Choreographer
▪ FrameCallback
▪ Delivered during the next
frame’s animation callback
▪ Measure the difference
between two inputs
VSync
Input
Animation
Draw
17ms 17ms17ms

8. Choreographer
VSync
Input
Animation
Draw
17ms 33ms17ms
draw draw drawdrop draw
17ms

9. public
interface
FrameCallback
{
/**
*
@param
frameTimeNanos
The
time
in
nanoseconds
when
the
frame
started
being
rendered
*/
void
doFrame(long
frameTimeNanos);
}

10. mFPSMeasuringCallback
=
new
Choreographer.FrameCallback()
{
@Override
public
void
doFrame(long
frameTimeNanos)
{
long
frameTimeMs
=
nsToMs(frameTimeNanos);
if
(mLastFrameTimeMs
==
FIRST_FRAME)
{
mLastFrameTimeMs
=
frameTimeMs;
mChoreographer.postFrameCallback(mFPSMeasuringCallback);
return;
}
long
milliSecondDelay
=
frameTimeMs
-­‐
mLastFrameTimeMs;
mLastFrameTimeMs
=
frameTimeMs;
onFrameRendered(milliSecondDelay);
mChoreographer.postFrameCallback(mFPSMeasuringCallback);
}
};
First frame!
Report time between frames
Always post the callback

11. An FPS measuring API
public
void
enable()
{
mLastFrameTimeMs
=
FIRST_FRAME;
mChoreographer.postFrameCallback(mFPSMeasuringCallback);
}
public
void
disable()
{
mChoreographer.removeFrameCallback(mFPSMeasuringCallback);
report();
}

12. A Reasonable Metric

13. Percent time spent dropping 2+ frames*
VSync
Input
Animation
Draw
0
<2 dropped frames = 6/11 = 55%
2+ dropped frames = 5/11 = 45%
4 dropped* 1 dropped 0 0 0
*rendered on the 5th frame
*…reasonable?

14. How does Facebook blame jank?

15. AutoBlame
▪ Must be lightweight
▪ High level
▪ Will not blame every slow frame
▪ Not perfect
VSync
Input
Animation
Draw
Expensive Work Marker

16. AutoBlame*
Year Class Slow time GC getView notifyDSC
2012 16% 6% 50% 16%
2014 22% 12% 44% 12%
*surprisingly accurate

17. AutoProfiler
VSync
Input
Animation
Draw
Expensive Work

18. AutoProfiler*
Method Time
com/android/widget/RecyclerView.onScrolled 16%
> com/facebook/logging/FeedLogger.onScroll 10%
> com/facebook/feed/NewsFeedFragment.maybeFetch 3.3%
>> com/facebook/feed/NewsFeedRecyclerView.notifyDataSetChange 3%
>> com/facebook/feed/FetchController.shouldFetch .3%
> com/facebook/prefetch/ImagePrefetcher.onScroll 2.7%
*totally made up shit

19. AutoProfiler
for
i
in
range(20):
time.sleep(1)
device.drag((start_x,
start_y),
(stop_x,
stop_y),
0.1,
15)
Traceview sample based profiling
MonkeyRunner Script
Left as an exercise to the developer Post-process Traceview file

20. Systrace
▪ Add your own markers
▪ Sample base profiling
VSync
Input
Animation
Draw
Expensive Work
Marker

21. How can I quickly improve performance?
▪ Ideal Profiling Device
▪ Nexus 4
▪ KitKat
▪ Systrace
▪ Custom markers for problem areas
▪ Sample based profiling
▪ Find an interaction or event which consistently causes lag or jitter
and profile it

22. Questions?
jsendros