"Motion Blur: TileMax" is too slow

[yvt]

2.135ms sounds too slow for such a simple operation.

materials
WebGL 1.0 (OpenGL ES 2.0 Chromium)
ATI Technologies Inc., AMD Radeon R9 M295X OpenGL Engine
Hyper.WebGLHyperRenderer 0.0.0 @ 1920x1080, Full HDR

Phase	Time
Frame	15633000	▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓
├ Before Render	0	░░░░░░░░░░░░░░░░░░░░
├ Render	15633000	▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓
│├ Motion Blur: TileMax	2135000	▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓
│├ Motion Blur: NeighborMax	13000	▓░░░░░░░░░░░░░░░░░░░
│├ Motion Blur: NeighborMax	12000	▓░░░░░░░░░░░░░░░░░░░
│├ Motion Blur: Final Pass	287000	▓▓▓▓░░░░░░░░░░░░░░░░