Implement PagedAttention V2 (#1348)

benchmarks/kernels/benchmark_paged_attention.py

@@ -0,0 +1,197 @@
+import argparse
+import random
+import time
+
+import torch
+
+from vllm import attention_ops
+
+NUM_BLOCKS = 1024
+PARTITION_SIZE = 512
+
+
+@torch.inference_mode()
+def main(
+    version: str,
+    num_seqs: int,
+    context_len: int,
+    num_query_heads: int,
+    num_kv_heads: int,
+    head_size: int,
+    use_alibi: bool,
+    block_size: int,
+    dtype: torch.dtype,
+    seed: int,
+    do_profile: bool,
+) -> None:
+    random.seed(seed)
+    torch.random.manual_seed(seed)
+    torch.cuda.manual_seed(seed)
+
+    scale = float(1.0 / (head_size**0.5))
+    query = torch.empty(num_seqs,
+                        num_query_heads,
+                        head_size,
+                        dtype=dtype,
+                        device="cuda")
+    query.uniform_(-scale, scale)
+
+    assert num_query_heads % num_kv_heads == 0
+    num_queries_per_kv = num_query_heads // num_kv_heads
+    head_mapping = torch.repeat_interleave(
+        torch.arange(num_kv_heads, dtype=torch.int32, device="cuda"),
+        num_queries_per_kv)
+    alibi_slopes = None
+    if use_alibi:
+        alibi_slopes = torch.randn(num_query_heads,
+                                   dtype=torch.float,
+                                   device="cuda")
+
+    context_lens = [context_len for _ in range(num_seqs)]
+    max_context_len = max(context_lens)
+    context_lens = torch.tensor(context_lens, dtype=torch.int, device="cuda")
+
+    # Create the block tables.
+    max_num_blocks_per_seq = (max_context_len + block_size - 1) // block_size
+    block_tables = []
+    for _ in range(num_seqs):
+        block_table = [
+            random.randint(0, NUM_BLOCKS - 1)
+            for _ in range(max_num_blocks_per_seq)
+        ]
+        block_tables.append(block_table)
+    block_tables = torch.tensor(block_tables, dtype=torch.int, device="cuda")
+
+    # Create the KV cache.
+    x = 16 // torch.tensor([], dtype=dtype).element_size()
+    key_cache_shape = (NUM_BLOCKS, num_kv_heads, head_size // x, block_size, x)
+    key_cache = torch.empty(size=key_cache_shape, dtype=dtype, device="cuda")
+    key_cache.uniform_(-scale, scale)
+    value_cache_shape = (NUM_BLOCKS, num_kv_heads, head_size, block_size)
+    value_cache = torch.empty(size=value_cache_shape,
+                              dtype=dtype,
+                              device="cuda")
+    value_cache.uniform_(-scale, scale)
+
+    # Prepare for the paged attention kernel.
+    output = torch.empty_like(query)
+    if version == "v2":
+        num_partitions = ((max_context_len + PARTITION_SIZE - 1) //
+                          PARTITION_SIZE)
+        tmp_output = torch.empty(
+            size=(num_seqs, num_query_heads, num_partitions, head_size),
+            dtype=output.dtype,
+            device=output.device,
+        )
+        exp_sums = torch.empty(
+            size=(num_seqs, num_query_heads, num_partitions),
+            dtype=torch.float32,
+            device=output.device,
+        )
+        max_logits = torch.empty_like(exp_sums)
+
+    def run_benchmark(num_iters: int, profile: bool = False) -> float:
+        torch.cuda.synchronize()
+        if profile:
+            torch.cuda.cudart().cudaProfilerStart()
+        start_time = time.perf_counter()
+
+        for _ in range(num_iters):
+            if version == "v1":
+                attention_ops.paged_attention_v1(
+                    output,
+                    query,
+                    key_cache,
+                    value_cache,
+                    head_mapping,
+                    scale,
+                    block_tables,
+                    context_lens,
+                    block_size,
+                    max_context_len,
+                    alibi_slopes,
+                )
+            elif version == "v2":
+                attention_ops.paged_attention_v2(
+                    output,
+                    exp_sums,
+                    max_logits,
+                    tmp_output,
+                    query,
+                    key_cache,
+                    value_cache,
+                    head_mapping,
+                    scale,
+                    block_tables,
+                    context_lens,
+                    block_size,
+                    max_context_len,
+                    alibi_slopes,
+                )
+            else:
+                raise ValueError(f"Invalid version: {version}")
+        torch.cuda.synchronize()
+
+        end_time = time.perf_counter()
+        if profile:
+            torch.cuda.cudart().cudaProfilerStart()
+        return (end_time - start_time) / num_iters
+
+    # Warmup.
+    print("Warming up...")
+    run_benchmark(num_iters=3, profile=False)
+
+    # Benchmark.
+    if do_profile:
+        latency = run_benchmark(num_iters=1, profile=True)
+    else:
+        latency = run_benchmark(num_iters=100, profile=False)
+    print(f"Kernel running time: {latency * 1000000:.3f} us")
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser(
+        description="Benchmark the paged attention kernel.")
+    parser.add_argument("--version",
+                        type=str,
+                        choices=["v1", "v2"],
+                        default="v2")
+    parser.add_argument("--batch-size", type=int, default=8)
+    parser.add_argument("--context-len", type=int, default=4096)
+    parser.add_argument("--num-query-heads", type=int, default=64)
+    parser.add_argument("--num-kv-heads", type=int, default=8)
+    parser.add_argument("--head-size",
+                        type=int,
+                        choices=[64, 80, 96, 112, 128, 256],
+                        default=128)
+    parser.add_argument("--block-size", type=int, choices=[16, 32], default=16)
+    parser.add_argument("--use-alibi", action="store_true")
+    parser.add_argument("--dtype",
+                        type=str,
+                        choices=["half", "bfloat16", "float"],
+                        default="half")
+    parser.add_argument("--seed", type=int, default=0)
+    parser.add_argument("--profile", action="store_true")
+    args = parser.parse_args()
+    print(args)
+
+    if args.num_query_heads % args.num_kv_heads != 0:
+        raise ValueError("num_query_heads must be divisible by num_kv_heads")
+    dtype_to_torch_dtype = {
+        "half": torch.half,
+        "bfloat16": torch.bfloat16,
+        "float": torch.float,
+    }
+    main(
+        version=args.version,
+        num_seqs=args.batch_size,
+        context_len=args.context_len,
+        num_query_heads=args.num_query_heads,
+        num_kv_heads=args.num_kv_heads,
+        head_size=args.head_size,
+        block_size=args.block_size,
+        use_alibi=args.use_alibi,
+        dtype=dtype_to_torch_dtype[args.dtype],
+        seed=args.seed,
+        do_profile=args.profile,
+    )

csrc/attention.cpp

@@ -1,7 +1,7 @@
 #include <torch/extension.h>
 #include <c10/util/Optional.h>
 
-void single_query_cached_kv_attention(
+void paged_attention_v1(
   torch::Tensor& out,
   torch::Tensor& query,
   torch::Tensor& key_cache,
@@ -14,9 +14,29 @@ void single_query_cached_kv_attention(
   int max_context_len,
   const c10::optional<torch::Tensor>& alibi_slopes);
 
+void paged_attention_v2(
+  torch::Tensor& out,
+  torch::Tensor& exp_sums,
+  torch::Tensor& max_logits,
+  torch::Tensor& tmp_out,
+  torch::Tensor& query,
+  torch::Tensor& key_cache,
+  torch::Tensor& value_cache,
+  torch::Tensor& head_mapping,
+  float scale,
+  torch::Tensor& block_tables,
+  torch::Tensor& context_lens,
+  int block_size,
+  int max_context_len,
+  const c10::optional<torch::Tensor>& alibi_slopes);
+
 PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
   m.def(
-    "single_query_cached_kv_attention",
-    &single_query_cached_kv_attention,
-    "Compute the attention between an input query and the cached key/value tensors");
+    "paged_attention_v1",
+    &paged_attention_v1,
+    "Compute the attention between an input query and the cached keys/values using PagedAttention.");
+  m.def(
+    "paged_attention_v2",
+    &paged_attention_v2,
+    "PagedAttention V2.");
 }