occupancy

Occupancy is a means, and the end is enough bytes in flight to cover memory latency. Little's law gives the number of loads an SM needs outstanding; the register file gives the warps you can afford; the kernels that win on H100 usually run at 25% to 50% occupancy with big tiles and no spills.

Occupancy is how many warps an SM holds against its maximum, and it is a means, not an end. The arithmetic from registers per thread to resident warps, the launch bound that caps registers and the spills that follow, the profiler's occupancy view, and the kernel where halving occupancy doubled speed.

Four sections, read in a fixed order, and one number that usually names the bottleneck outright. The report of a kernel at 12 percent of DRAM bandwidth while its memory pipeline reads 82 percent busy, what that gap means, the fix it implies, and the numbers the fixed kernel reports back.

Registers are allocated in fixed steps out of a fixed budget per multiprocessor, so a small increase in live values can cost a whole resident block. The compiler output that shows it in two lines, the occupancy cliff arithmetic, and the two different failure modes that produce the same symptom.