ISP Pixel Load
What does this counter show?
Percentage of the time that the ISP pixel-processing is busy.
What does a high value mean?
It would mean that a large quantity of non-visible (non-shaded) pixels are being processed. These may be hidden due to:
The depth/stencil test (e.g. hidden behind an opaque object).
A process may be rendering triangles that update only the depth/stencil buffer (and not any colour buffer).