Add FP4 Indexer for DeepSeek V4 on SM120 (#27059)

python/sglang/srt/layers/attention/deepseek_v4_backend.py

@@ -650,6 +650,11 @@ class DeepseekV4AttnBackend(
             page_size=self.page_size,
             page_table=core_attn_metadata.page_table,
             c4_seq_lens=core_attn_metadata.c4_topk_lengths_raw,
+            # The SM120 FP4 kernel schedules split_kv=128, while the generic
+            # JIT metadata planner encodes split_kv=256.
+            force_deep_gemm_metadata=(
+                self.enable_deepseek_v4_fp4_indexer and _is_sm120
+            ),
             use_prefill_cuda_graph=use_prefill_cuda_graph,
         )
 

python/sglang/srt/layers/attention/dsv4/metadata.py

@@ -112,6 +112,7 @@ class PagedIndexerMetadata:
     page_size: int
     page_table: torch.Tensor
     c4_seq_lens: torch.Tensor
+    force_deep_gemm_metadata: bool = False
     use_prefill_cuda_graph: bool = False
     deep_gemm_metadata: Any = field(init=False, repr=False)
     topk_metadata: torch.Tensor = field(init=False, repr=False)
@@ -124,12 +125,12 @@ class PagedIndexerMetadata:
             envs.SGLANG_FP8_PAGED_MQA_LOGITS_TORCH.get()
             or is_xpu()
             or envs.SGLANG_OPT_USE_AITER_INDEXER.get()
-        ):
+        ) and not self.force_deep_gemm_metadata:
             self.deep_gemm_metadata = None
         else:
             import deep_gemm
 
-            use_jit_indexer = (
+            use_jit_indexer = not self.force_deep_gemm_metadata and (
                 envs.SGLANG_OPT_USE_JIT_INDEXER_METADATA.get()
                 or self.c4_seq_lens.numel() > _LARGE_INDEXER_QUERY_THRESHOLD
             )
@@ -183,7 +184,11 @@ class PagedIndexerMetadata:
         copy_metadata(
             src=other,
             dst=self,
-            check_eq_fields=["page_size", "use_prefill_cuda_graph"],
+            check_eq_fields=[
+                "page_size",
+                "force_deep_gemm_metadata",
+                "use_prefill_cuda_graph",
+            ],
             copy_fields=copy_fields,
             assign_fields=assign_fields,
         )

python/sglang/srt/server_args.py

@@ -7263,9 +7263,11 @@ class ServerArgs:
                     "Debug mode for CUDA graph is enabled via breakable CUDA graph. "
                     "All operations will run eagerly through the graph capture/replay path."
                 )
-        if self.enable_deepseek_v4_fp4_indexer and not is_sm100_supported():
+        if self.enable_deepseek_v4_fp4_indexer and not (
+            is_sm100_supported() or is_sm120_supported()
+        ):
             raise ValueError(
-                "--enable-deepseek-v4-fp4-indexer requires SM100 GPUs with "
+                "--enable-deepseek-v4-fp4-indexer requires SM100 or SM120 GPUs with "
                 "DeepGEMM FP4 indexer support."
             )
         # FP8 W_o GEMM needs DeepGEMM JIT. Enable exactly where the runtime can run

test/registered/kernels/benchmark/attention/bench_dsv4_fp4_indexer.py

@@ -7,11 +7,14 @@ import triton
 
 from sglang.benchmark.bench_utils import run_bench
 from sglang.kernels.jit.benchmark.utils import get_benchmark_range
-from sglang.srt.utils import is_sm100_supported
+from sglang.srt.utils import is_sm100_supported, is_sm120_supported
 from sglang.test.ci.ci_register import register_cuda_ci
 
 register_cuda_ci(
-    est_time=5, stage="base-b-kernel-benchmark", runner_config="1-gpu-large"
+    est_time=5,
+    stage="base-b-kernel-benchmark",
+    runner_config="1-gpu-large",
+    disabled="Temporarily disabled until DeepGEMM is ready",
 )
 
 try:
@@ -167,8 +170,8 @@ def benchmark(batch: int, seq_len_kv: int, provider: str):
 
 
 if __name__ == "__main__":
-    if not is_sm100_supported():
-        print("[skip] DeepSeek V4 FP4 indexer benchmark requires SM100 CUDA.")
+    if not (is_sm100_supported() or is_sm120_supported()):
+        print("[skip] DeepSeek V4 FP4 indexer benchmark requires SM100 or SM120 CUDA.")
         sys.exit(0)
     if deep_gemm is None or per_token_cast_to_fp4 is None:
         print("[skip] DeepGEMM is unavailable.")

test/registered/unit/layers/test_dsv4_nonpaged_indexer.py

@@ -7,7 +7,10 @@ import torch
 
 from sglang.srt.environ import envs
 from sglang.srt.layers.attention.dsv4.indexer import FP8_DTYPE, C4IndexerBackendMixin
-from sglang.srt.layers.attention.dsv4.metadata import NonPagedIndexerPlan
+from sglang.srt.layers.attention.dsv4.metadata import (
+    NonPagedIndexerPlan,
+    PagedIndexerMetadata,
+)
 from sglang.srt.model_executor.forward_batch_info import ForwardMode
 from sglang.srt.runtime_context import get_parallel
 from sglang.test.ci.ci_register import register_cpu_ci
@@ -18,6 +21,54 @@ register_cpu_ci(est_time=2, suite="base-a-test-cpu")
 _INDEXER = "sglang.srt.layers.attention.dsv4.indexer"
 
 
+class TestDSV4PagedIndexerMetadata(CustomTestCase):
+    def test_sm120_fp4_forces_deep_gemm_metadata(self):
+        expected = torch.tensor([[0, 0], [1, 0]], dtype=torch.int32)
+        deep_gemm = SimpleNamespace(
+            get_num_sms=MagicMock(return_value=1),
+            get_paged_mqa_logits_metadata=MagicMock(return_value=expected),
+        )
+
+        with (
+            patch.dict(sys.modules, {"deep_gemm": deep_gemm}),
+            envs.SGLANG_FP8_PAGED_MQA_LOGITS_TORCH.override(True),
+            envs.SGLANG_OPT_USE_AITER_INDEXER.override(False),
+            envs.SGLANG_OPT_USE_JIT_INDEXER_METADATA.override(True),
+            envs.SGLANG_OPT_USE_TOPK_V2.override(False),
+            patch(
+                "sglang.kernels.ops.attention.dsv4.get_paged_mqa_logits_metadata"
+            ) as jit_metadata,
+        ):
+            metadata = PagedIndexerMetadata(
+                page_size=256,
+                page_table=torch.zeros((1, 1), dtype=torch.int32),
+                c4_seq_lens=torch.tensor([65], dtype=torch.int32),
+                force_deep_gemm_metadata=True,
+            )
+
+        self.assertIs(metadata.deep_gemm_metadata, expected)
+        deep_gemm.get_num_sms.assert_called_once_with()
+        deep_gemm.get_paged_mqa_logits_metadata.assert_called_once()
+        args = deep_gemm.get_paged_mqa_logits_metadata.call_args.args
+        torch.testing.assert_close(args[0], torch.tensor([[65]], dtype=torch.int32))
+        self.assertEqual(args[1:], (64, 1))
+        jit_metadata.assert_not_called()
+
+    def test_sm120_fp8_torch_fallback_keeps_metadata_none(self):
+        with (
+            envs.SGLANG_FP8_PAGED_MQA_LOGITS_TORCH.override(True),
+            envs.SGLANG_OPT_USE_AITER_INDEXER.override(False),
+            envs.SGLANG_OPT_USE_TOPK_V2.override(False),
+        ):
+            metadata = PagedIndexerMetadata(
+                page_size=256,
+                page_table=torch.zeros((1, 1), dtype=torch.int32),
+                c4_seq_lens=torch.tensor([65], dtype=torch.int32),
+            )
+
+        self.assertIsNone(metadata.deep_gemm_metadata)
+
+
 class TestDSV4NonPagedIndexer(CustomTestCase):
     def _is_eligible(self, **overrides):
         backend = SimpleNamespace(hisparse_coordinator=None)