Interpretation of systrace and dumpsys

I'm trying to interpret the systrace for a video playback on ANdroid device.

Following are my observation.

1)I see both HW_VSYNC_0 and VsyncOn

2)HW_VSYNC_0 is not periodic

3)VsyncOn is periodic and periodicity is 33.33ms

Below are my questions

1)I'm confused as to why I see HW_VSYNC_0 and VsyncOn.

2)what is the difference between these two?

3)Why is the bar for HW_VSYNC_0 is not uniform?

4)However When I do dumsys on SurfaceFlinger I observe Vsync being disabled.But still why do I see VsynOn in systrace?

Below is part of dumpsys information.

Can anyone please light on how I can relate both the Information? Thanks in advance...

VSYNC state: disabled

soft-vsync: disabled

numListeners=9,

events-delivered: 85904

0xf8a1ab90: count=-1

0xf8a1ad70: count=-1

0xf8a1c2a0: count=-1

0xf8a1c7b0: count=-1

0xf8a1d8f0: count=-1

0xf8a3c480: count=-1

0xf8aba2b0: count=-1

0xf8b029f0: count=-1

0xf8b59ad0: count=-1

h/w composer state:

h/w composer present and enabled

Hardware Composer state (version 1030000):

mDebugForceFakeVSync=0

Display[0] : 1920x1200, xdpi=254.000000, ydpi=254.000000, refresh=16666666

numHwLayers=2, flags=00000000

type    |  handle  |   hints  |   flags  | tr | blend |  format  |          source 

crop | frame name ------------+----------+----------+----------+----+-------+----------+------------------- --------------+--------------------------------

    HWC | f8ac8a30 | 00000002 | 00000000 | 00 | 00100 | 7fa00f00 | [    0.0,    0.0, 

1920.0, 1080.0] | [ 0, 60, 1920, 1140] SurfaceView

FB TARGET | f8ad1ef0 | 00000000 | 00000000 | 00 | 00105 | 00000001 | [ 0.0, 0.0, 1920.0, 1200.0] | [ 0, 0, 1920, 1200] HWC_FRAMEBUFFER_TARGET