mali gpu counter

Hello, recently I am studying mali gpu counters and encountered some questions about the counter "primitive loaded" and "primitives dropped". I refer to the counter explaination here https://community.arm.com/docs/DOC-10182#jive_content_id_321_COMPUTE_TASKS .

It says the counter "Primitives loaded" increments for every primitive read from the tile list, but not all of these triangles will necessarily be visible in the current tile, due to the use of the hierarchical tiler. What does the counter mean? the number of triangles in one frame or the number of triangles in a single tile?  or maybe something else? Could you explain in detail?

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