[Perf] Skip trivial DSV4 nonpaged indexer logits (#33857)

Co-authored-by: weireweire <20922698+weireweire@users.noreply.github.com>
2026-08-13 16:21:30 -07:00
parent 151a314829
commit 54c44fef73
2 changed files with 20 additions and 5 deletions
@@ -585,6 +585,13 @@ class C4IndexerBackendMixin:
        ke = c4_seq_lens[:query_rows].reshape(-1).to(torch.int32).contiguous()
        gather_seq_lens = ke[-1:]
        ks = torch.zeros_like(ke)
+        # SGL Top-K synthesizes sequential indices for trivial rows without
+        # reading logits, so DeepGEMM can receive an empty range for them.
+        if (
+            self.dsa_topk_backend.is_sgl_kernel()
+            and not envs.SGLANG_TOPK_TRANSFORM_512_TORCH.get()
+        ):
+            ke = torch.where(ke - ks > c4_indexer.index_topk, ke, ks)
        c4_page_size = indexer_metadata.c4_page_size
        max_seqlen_k = (final_c4_len + c4_page_size - 1) // c4_page_size * c4_page_size
        plan = NonPagedIndexerPlan(