[None][perf] PDL on the missing decode edges - #17454
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…d it Median consumer-start minus producer-end on the main stream was -64 ns for the QKV GEMM into the fused producer and for the index-score kernel into the block selector, against roughly -400 ns on the edges that already overlap. Both consumers now launch with programmatic stream serialization and wait immediately before their first dependent load, so their index arithmetic runs in the producer's tail. Worth about 0.35 us per edge across 57 sparse layers. Behaviour is unchanged: cudaGridDependencySynchronize is a no-op when the kernel was not launched with PDL, and the launches follow getEnvEnablePDL as the rest of the codebase does. Signed-off-by: Balaram Buddharaju <169953907+brb-nv@users.noreply.github.com>
The scorer read seq_lens before griddepcontrol.wait. num_blocks derived from it bounds an unmasked block_table load and an unmasked score store, so a stale length is an out-of-bounds write, and seq_lens is patched every step by on_update_kv_lens. That was safe only because nothing between that patch and this kernel writes it. Move the load past the wait and leave the barrier init and descriptor prefetch ahead of it as the work PDL overlaps. Also drop the launch_dependents at kernel entry. It is not a visibility bug, since a consumer's wait blocks until this grid completes, but the only consumer is the block selector, which reduces over every block this grid writes and so cannot start early. Now that the selector is PDL-launched, triggering at entry only left it resident and spinning in its own wait for this kernel's whole lifetime. The implicit trigger as the CTAs exit still gives it the launch overlap. Signed-off-by: Balaram Buddharaju <169953907+brb-nv@users.noreply.github.com>
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