Read cub/agent/single_pass_scan_operators.cuh lines 136-148:
delay<Delay, GridThreshold=500>() {
if (gridDim.x < GridThreshold) __threadfence_block();
else __nanosleep(Delay);
}
BI-V100: 16 SMs × ~10 CTAs/SM = ~160 CTAs. Always < 500.
Therefore ALL delay strategies collapse to __threadfence_block().
The ns/dcid/l2w parameters are architectural no-ops on BI-V100.
This explains bench_bi100.py finding no_delay optimal — not a lucky
guess but a hard gate in CCCL's tile synchronization code. The
'ns×0.5, l2w×0.6' scaling was always computing values that would
never be used (delay() never reaches the __nanosleep branch).
Source: single_pass_scan_operators.cuh (full read, 200 lines)
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