The FS EU Stall metric represents the percentage of overall GPU time that the execution units (EUs) were stalled in Fragment Shader instructions.
This metric does not show total amount of stalled time in the fragment shader, but only the fraction of time when fragment shader stalls caused the entire EU to stall. The entire EU stalls when all of its threads are stalled.
- If FS EU Stall is 50%, it means that half of the overall GPU time was spent stalled on Fragment Shader instructions.
- If FS EU Stall is 0%, it means that no Fragment Shader was associated with selected rendering calls or Fragment Shader threads were not causing EU stalls.
- This metric is important if fragment shading seems to be the bottleneck for selected rendering calls. If FS EU Stall accounts for most of the EU active time, then to improve performance you might need to simplify the fragment shader.
- If FS EU Stall is larger than you expect and you are encountering slow rendering times, you need to concentrate on fragment shader code to find reasons for these stalls.