[None][fix] Self-sampling top-k host: physical row-width envelope and exact-row warmup population - #18683
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… exact-row warmup population _varlen_launcher inflated the envelope to max(min(n_env, npad), k + 1) and passed it to the reg / reg_clus / clus launch tuples; the kernels clamp each row's valid length to that envelope before the short-path decision, so logits narrower than k + 1 with kv lengths beyond k read k + 1 elements at the physical row stride (into the next row, past the tensor for the last row). Only routing needs the k + 1 floor: the launch tuples now carry min(n_env, npad) and such rows take the short path. warmup_varlen keyed its done-set on the band representatives and returned before the exact-row launcher population, so a later call with a new row count inside an already-warmed band left that row count uncompiled and CUDA-graph capture at it raised. The done key now gates only the band launches; the exact-row population always runs. validate_run_ws now requires 16-byte base alignment, matching the DSL workspace fake. Neither defect is reachable through the TensorRT-LLM indexer path (its logits width, kv_lens and max_seq_len share one bound and graph launchers come from the eager warmup forwards); both hit direct callers of run_varlen / warmup_varlen (DKG issue NVIDIA#60). Made-with: Claude Code (Fable 5.1) Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Signed-off-by: longcheng-nv <243710427+longcheng-nv@users.noreply.github.com>
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Included review availability: Your plan provides up to 12 included reviews per hour; 10 remain after this review. WalkthroughVarlen Top-K decoding now clamps physical kernel bounds to row width, requires 16-byte workspace alignment, and populates launcher-cache entries incrementally during warmup. Regression tests cover the updated routing, warmup behavior, and alignment validation. ChangesVarlen Top-K launcher corrections
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: ⚪ Minimal · up to This change corrects varlen Top-K launch bounds, warmup launcher population, and workspace alignment validation, with regression coverage described for each behavior. No evidenced merge-blocking risk remains. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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In `@tests/unittest/_torch/thop/parallel/test_gvr_selfsampling_topk.py`:
- Line 956: Add -> None return annotations to the three test functions
test_selfsampling_varlen_narrow_logits_clamps_envelope_to_row_width,
test_selfsampling_warmup_incremental_rows_populate_exact_launchers, and
test_validate_run_ws_requires_16_byte_alignment in
tests/unittest/_torch/thop/parallel/test_gvr_selfsampling_topk.py at lines 956,
978, and 1002.
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Picks up the main-side waive of unittest/_torch/visual_gen/test_trtllm_serve_endpoints.py (NVIDIA#18685) that failed the CPU lanes in the previous CI round. Made-with: Claude Code (Fable 5.1) Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Signed-off-by: longcheng-nv <243710427+longcheng-nv@users.noreply.github.com>
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Picks up the main-side waive of unittest/_torch/visual_gen/test_trtllm_serve_e2e.py TestFlux1/Flux2TextToImage (nvbugs/6720944) that failed the DGX_B200 lane in the previous CI round. Made-with: Claude Code (Fable 5.1) Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Signed-off-by: longcheng-nv <243710427+longcheng-nv@users.noreply.github.com>
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2 participants
Dev Engineer Review
k + 1floor only to routing decisions.warmup_varlento populate exact-row launchers within warmed bands.QA Engineer Review
test_selfsampling_varlen_narrow_logits_clamps_envelope_to_row_width.test_selfsampling_warmup_incremental_rows_populate_exact_launchers.test_validate_run_ws_requires_16_byte_alignment.tests/integration/test_lists/for CI or manual QA coverage.Description
Two host-side defects in the self-sampling GVR varlen path, found by the FlashInfer port review (DKG issue #60) and reproduced against the shared host code at #18625's head:
_varlen_launchercomputedmax(min(n_env, npad), k + 1)and passed it as the envelope slot of the reg / reg_clus / clus launch tuples. The kernels clamp each row's kv-derived valid length to that envelope before the short-path decision, so a caller whose logits are narrower thank + 1while somekv_lensexceedkmade the row load run tok + 1elements at the physical row stride: into the next row, and past the tensor for the last row (compute-sanitizer reports the out-of-bounds reads; with the caching allocator only the wrong result shows). The router still needs thek + 1floor to pick a non-degenerate family, so the launch tuples now carry the physical boundmin(n_env, npad)and only routing seesmax(that, k + 1). A row whose valid length exceeds the physical width now clamps to it and takes the in-kernel short path (identity +-1tail), which is the documented contract.warmup_varlenkeyed its done-set on the band representatives and returned before the exact-row launcher population, so a later call with a new row count inside an already-warmed band never created that row count's launcher, and a CUDA-graph capture at it raised "varlen launcher not compiled for this shape". The done key now gates only the GPU band launches; the exact-row population (pure host work, compile-cache hits) always runs.Also tightens
validate_run_wsfrom 8- to 16-byte base alignment to match the DSL workspace fake, so a misaligned workspace fails on the host with a clear message instead of at DSL conversion.TensorRT-LLM's own indexer path cannot reach either defect: its logits width,
kv_lensandmax_seq_lenall derive from the samekv_cache_manager.max_seq_len, so every row's valid length fits the row width, and CUDA-graph launchers come from the eager warmup forwards rather thanwarmup_varlen. Both are real for direct callers ofrun_varlen/warmup_varlen(the FlashInfer port, op-level benchmarks). Whenever the logits width is at leastk + 1the launch tuples are bit-identical to before, so there is no performance change on the production path.Test Coverage
tests/unittest/_torch/thop/parallel/test_gvr_selfsampling_topk.py:test_selfsampling_varlen_narrow_logits_clamps_envelope_to_row_width— narrow logits withkv_lensbeyondk(and exactly the width): identity +-1tail per row, launch envelope equals the row width.test_selfsampling_warmup_incremental_rows_populate_exact_launchers— incrementalwarmup_varlenrow lists, then a CUDA-graph capture at the new row count.test_validate_run_ws_requires_16_byte_alignment.Full module passes locally on B200 (sm_100).
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