Optimize the update flashinfer indices (#1262)

python/sglang/srt/model_executor/forward_batch_info.py

@@ -22,6 +22,8 @@ from typing import TYPE_CHECKING, List
 
 import numpy as np
 import torch
+import triton
+import triton.language as tl
 
 from sglang.srt.managers.schedule_batch import ScheduleBatch
 from sglang.srt.mem_cache.memory_pool import BaseTokenToKVPool, ReqToTokenPool
@@ -262,6 +264,42 @@ class InputMetadata:
         )
 
 
+@triton.jit
+def create_flashinfer_kv_indices_triton(
+    req_to_token_ptr,  # [max_batch, max_context_len]
+    req_pool_indices_ptr,
+    page_kernel_lens_ptr,
+    kv_indptr,
+    kv_start_idx,
+    max_context_len,
+    kv_indices_ptr,
+):
+    BLOCK_SIZE: tl.constexpr = 512
+    pid = tl.program_id(axis=0)
+    req_pool_index = tl.load(req_pool_indices_ptr + pid)
+    kv_indices_offset = tl.load(kv_indptr + pid)
+
+    kv_start = 0
+    kv_end = 0
+    if kv_start_idx:
+        kv_start = tl.load(kv_start_idx + pid).to(tl.int32)
+        kv_end = kv_start
+    kv_end += tl.load(page_kernel_lens_ptr + pid).to(tl.int32)
+
+    req_to_token_ptr += req_pool_index * max_context_len
+    kv_indices_ptr += kv_indices_offset
+
+    ld_offset = kv_start + tl.arange(0, BLOCK_SIZE)
+    st_offset = tl.arange(0, BLOCK_SIZE)
+    num_loop = tl.cdiv(kv_end - kv_start, BLOCK_SIZE)
+    for _ in range(num_loop):
+        mask = ld_offset < kv_end
+        data = tl.load(req_to_token_ptr + ld_offset, mask=mask)
+        tl.store(kv_indices_ptr + st_offset, data, mask=mask)
+        ld_offset += BLOCK_SIZE
+        st_offset += BLOCK_SIZE
+
+
 def update_flashinfer_indices(
     forward_mode,
     model_runner,
@@ -285,17 +323,18 @@ def update_flashinfer_indices(
 
         kv_indptr = torch.zeros((batch_size + 1,), dtype=torch.int32, device="cuda")
         kv_indptr[1:] = torch.cumsum(paged_kernel_lens, dim=0)
-        req_pool_indices_cpu = req_pool_indices.cpu().numpy()
-        paged_kernel_lens_cpu = paged_kernel_lens.cpu().numpy()
-        kv_indices = torch.cat(
-            [
-                model_runner.req_to_token_pool.req_to_token[
-                    req_pool_indices_cpu[i], : paged_kernel_lens_cpu[i]
-                ]
-                for i in range(batch_size)
-            ],
-            dim=0,
-        ).contiguous()
+
+        kv_indices = torch.empty(kv_indptr[-1], dtype=torch.int32, device="cuda")
+        create_flashinfer_kv_indices_triton[(batch_size,)](
+            model_runner.req_to_token_pool.req_to_token,
+            req_pool_indices,
+            paged_kernel_lens,
+            kv_indptr,
+            None,
+            model_runner.req_to_token_pool.req_to_token.size(1),
+            kv_indices,
+        )
+
         kv_last_page_len = torch.ones((batch_size,), dtype=torch.int32, device="cuda")
 
         if forward_mode == ForwardMode.DECODE:
@@ -365,18 +404,17 @@ def update_flashinfer_indices(
 
             kv_indptr = torch.zeros((batch_size + 1,), dtype=torch.int32, device="cuda")
             kv_indptr[1:] = torch.cumsum(paged_kernel_lens, dim=0)
-            req_pool_indices_cpu = req_pool_indices.cpu().numpy()
-            paged_kernel_lens_cpu = paged_kernel_lens.cpu().numpy()
-            kv_indices = torch.cat(
-                [
-                    model_runner.req_to_token_pool.req_to_token[
-                        req_pool_indices_cpu[i],
-                        kv_start_idx[i] : kv_start_idx[i] + paged_kernel_lens_cpu[i],
-                    ]
-                    for i in range(batch_size)
-                ],
-                dim=0,
-            ).contiguous()
+
+            kv_indices = torch.empty(kv_indptr[-1], dtype=torch.int32, device="cuda")
+            create_flashinfer_kv_indices_triton[(batch_size,)](
+                model_runner.req_to_token_pool.req_to_token,
+                req_pool_indices,
+                paged_kernel_lens,
+                kv_indptr,
+                kv_start_idx,
+                model_runner.req_to_token_pool.req_to_token.size(1),
+                kv_indices,
+            )
 
             if forward_mode == ForwardMode.DECODE:
                 # CUDA graph uses different flashinfer_decode_wrapper

test/srt/test_create_kvindices.py

@@ -0,0 +1,76 @@
+import itertools
+import unittest
+
+import numpy as np
+import torch
+
+from sglang.srt.model_executor.forward_batch_info import (
+    create_flashinfer_kv_indices_triton,
+)
+
+
+class TestCreateKvIndices(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        if not torch.cuda.is_available():
+            raise unittest.SkipTest("CUDA is not available")
+        torch.set_default_device("cuda")
+
+    def _run_test(self, batch, max_batch, max_context_len):
+        req_to_token = torch.arange(
+            max_batch * max_context_len, dtype=torch.int32, device="cuda"
+        ).reshape((max_batch, max_context_len))
+        req_pool_indices = torch.tensor(
+            torch.from_numpy(
+                np.random.choice(range(max_batch), size=batch, replace=False)
+            ),
+            dtype=torch.int32,
+            device="cuda",
+        )
+        paged_kernel_lens = torch.tensor(
+            torch.from_numpy(
+                np.random.choice(range(max_context_len), size=batch, replace=False)
+            ),
+            dtype=torch.int32,
+            device="cuda",
+        )
+
+        kv_indptr = torch.zeros((batch + 1,), dtype=torch.int32, device="cuda")
+        kv_indptr[1:] = torch.cumsum(paged_kernel_lens, dim=0)
+
+        # ref
+        req_pool_indices_cpu = req_pool_indices.cpu().numpy()
+        paged_kernel_lens_cpu = paged_kernel_lens.cpu().numpy()
+        kv_indices_ref = torch.cat(
+            [
+                req_to_token[req_pool_indices_cpu[i], : paged_kernel_lens_cpu[i]]
+                for i in range(batch)
+            ],
+            dim=0,
+        ).contiguous()
+
+        # triton
+        kv_indices_triton = torch.empty(kv_indptr[-1], dtype=torch.int32, device="cuda")
+        create_flashinfer_kv_indices_triton[(batch,)](
+            req_to_token,
+            req_pool_indices,
+            paged_kernel_lens,
+            kv_indptr,
+            None,
+            req_to_token.size(1),
+            kv_indices_triton,
+        )
+
+        # Check
+        self.assertTrue(torch.equal(kv_indices_ref, kv_indices_triton))
+
+    def test_create_kvindices(self):
+        BATCH = [1, 37, 1786]
+        MAX_BATCH = 4096
+        MAX_CONTEXT_LEN = 4096
+        for batch in BATCH:
+            self._run_test(batch, MAX_BATCH, MAX_CONTEXT_LEN)
+
+
+if __name__ == "__main__":
+    unittest.main()