When building a simple Pong game with JavaFX, I noticed that even the simplest animation is jerky. The test case below should illustrate that:

public class AnimationTest extends Application
{
    private static final double WIDTH = 1000;
    private static final double HEIGHT = 600;
    private static final double SIZE = 10;
        
    @Override
    public void start(Stage stage)
    {
        Rectangle rectangle = new Rectangle(SIZE, SIZE);
        rectangle.setTranslateX(0);
        rectangle.setTranslateY((HEIGHT - SIZE) / 2);
        
        Scene scene = new Scene(new Group(rectangle), WIDTH, HEIGHT);
        stage.setScene(scene);
        stage.show();
        
        new AnimationTimer()
        {
            private boolean goingRight = true;
            
            @Override
            public void handle(long now)
            {
                rectangle.setTranslateX(rectangle.getTranslateX() + (goingRight ? 3 : -3));
                if (rectangle.getTranslateX() > WIDTH - SIZE) {
                    rectangle.setTranslateX(WIDTH - SIZE);
                    goingRight = false;
                } else if (rectangle.getTranslateX() < 0) {
                    rectangle.setTranslateX(0);
                    goingRight = true;
                }
            }
        }.start();
    }
    
    public static void main(String... args)
    {
        Application.launch(AnimationTest.class, args);
    }
}

If I add frame measuring to the AnimationTimer, I notice that most frames last about 16ms, but once in a while a frame comes along that lasts anywhere from 30ms up to 120ms. When running this test case with pulse logger on, I noticed similar issues, for example:

PULSE: 144 [17ms:31ms]
T12 (0 +0ms): CSS Pass
T12 (0 +0ms): Layout Pass
T12 (0 +0ms): Waiting for previous rendering
T12 (0 +0ms): Copy state to render graph
T10 (0 +0ms): Dirty Opts Computed
T10 (0 +1ms): Render Roots Discovered
T10 : 1 different dirty regions to render
T10 : Dirty Region 0: RectBounds { minX:429.0, minY:295.0, maxX:442.0, maxY:305.0} (w:13.0, h:10.0)
T10 : Render Root Path 0: [com.sun.javafx.sg.prism.NGGroup@6d1692fd]
T10 (1 +0ms): Painted
T10 (1 +30ms): Presentable.present
T10 (31 +0ms): Finished Presenting Painter
Counters:
Nodes rendered: 2
Nodes visited during render: 2

[145 17ms:15ms][146 16ms:1ms][147 17ms:2ms][148 17ms:13ms][149 16ms:7ms][150 17ms:5ms][151 16ms:2ms][152 18ms:1ms][153 16ms:2ms][154 16ms:2ms][155 17ms:2ms][156 17ms:2ms][157 16ms:1ms][158 17ms:1ms][159 17ms:1ms][160 17ms:0ms][161 16ms:3ms][162 17ms:2ms][163 17ms:2ms][164 17ms:0ms]
[165 16ms:1ms][166 16ms:1ms][167 17ms:1ms][168 17ms:2ms][169 16ms:7ms][170 17ms:4ms][171 17ms:2ms][172 16ms:3ms][173 17ms:2ms][174 17ms:1ms][175 17ms:1ms][176 17ms:1ms][177 17ms:2ms][178 15ms:2ms][179 17ms:2ms][180 17ms:2ms][181 16ms:1ms][182 17ms:1ms][183 17ms:2ms][184 16ms:2ms]
[185 17ms:2ms][186 17ms:2ms][187 16ms:3ms][188 17ms:2ms][189 17ms:2ms][190 16ms:2ms][191 17ms:2ms][192 17ms:2ms][193 16ms:3ms][194 17ms:2ms][195 17ms:3ms][196 17ms:7ms][197 16ms:2ms][198 17ms:2ms][199 17ms:2ms][200 16ms:2ms][201 17ms:0ms][202 16ms:1ms][203 17ms:1ms][204 17ms:1ms]
[205 16ms:2ms][206 17ms:2ms][207 17ms:1ms][208 16ms:3ms][209 17ms:2ms][210 17ms:3ms][211 16ms:2ms][212 18ms:15ms][213 16ms:0ms][214 17ms:2ms][215 16ms:2ms][216 17ms:1ms][217 16ms:2ms][218 18ms:2ms][219 16ms:2ms][220 18ms:2ms][221 16ms:2ms][222 16ms:2ms][223 17ms:2ms][224 16ms:2ms][225 17ms:0ms][226 16ms:1ms][227 17ms:2ms][228 18ms:3ms][229 17ms:0ms][230 15ms:3ms][231 17ms:2ms][232 17ms:2ms][233 16ms:3ms][234 18ms:0ms][235 15ms:2ms][236 17ms:2ms][237 17ms:2ms][238 16ms:1ms][239 17ms:1ms][240 17ms:2ms][241 16ms:2ms][242 17ms:2ms][243 17ms:3ms][244 16ms:1ms]
[245 18ms:1ms][246 16ms:1ms][247 16ms:2ms][248 17ms:2ms][249 17ms:2ms][250 16ms:6ms][251 19ms:1ms][252 15ms:2ms][253 18ms:2ms][254 15ms:6ms][255 17ms:2ms][256 16ms:3ms]

PULSE: 257 [18ms:30ms]
T12 (0 +0ms): CSS Pass
T12 (0 +0ms): Layout Pass
T12 (0 +0ms): Waiting for previous rendering
T12 (0 +0ms): Copy state to render graph
T10 (0 +0ms): Dirty Opts Computed
T10 (0 +0ms): Render Roots Discovered
T10 : 1 different dirty regions to render
T10 : Dirty Region 0: RectBounds { minX:768.0, minY:295.0, maxX:781.0, maxY:305.0} (w:13.0, h:10.0)
T10 : Render Root Path 0: [com.sun.javafx.sg.prism.NGGroup@6d1692fd]
T10 (1 +0ms): Painted
T10 (1 +29ms): Presentable.present
T10 (30 +0ms): Finished Presenting Painter
Counters:
Nodes rendered: 2
Nodes visited during render: 2

And so forth...

RT-13974 seems to be similar.