iOS GPU Counter indices description

GPU General Counter
a) VertexOccupancy：Measures how many vertex shader simdgroups are concurrently running in the GPU relative to the GPU’s maximum number of concurrently running simdgroups.

b) FragmentOccupancy：Measures how many fragment shader simdgroups are concurrently running in the GPU relative to the GPU’s maximum number of concurrently running simdgroups.

c) ComputeOccupancy：Measures how many compute shader simdgroups are concurrently running in the GPU relative to the GPU’s maximum number of concurrently running simdgroups.

GPU Memory Counter
a) BufferReadLimiter：Measures the time during which buffer loads are attempted to execute as a percentage of peak buffer load performance.

b) TextureSampleLimiter：Measures the time during which texture samples are attempted to execute as a percentage of peak texture sample performance.

c) GpuReadBandwidth：Measures how much memory, in gigabytes per second, are read by the GPU from a memory external to the GPU (potentially main memory).

d) GpuWriteBandwidth：Measures how much memory, in gigabytes per second, are written by the GPU to a memory external to the GPU (potentially main memory).

GPU Shader Counter
a) Alulimiter：Measures the time during which ALU work is attempted to execute as a percentage of peak ALU performance.