[Kernel] add triton kernels for sampling (vllm-project#4550)

### What this PR does / why we need it?
Replace pyorch implement of sampling with triton kernels

### Does this PR introduce _any_ user-facing change?
No


- vLLM version: v0.11.2

---------

Signed-off-by: Lord_of_Ironhill <[email protected]>
Signed-off-by: whx-sjtu <[email protected]>
Co-authored-by: Lord_of_Ironhill <[email protected]>
Co-authored-by: whx-sjtu <[email protected]>

Author: 3 people

vllm_ascend/sample/rejection_sampler.py

@@ -4,6 +4,7 @@
 import torch
 import torch.nn as nn
 import vllm.v1.sample.rejection_sampler as rs
+from vllm.triton_utils import HAS_TRITON, tl, triton
 from vllm.v1.sample.metadata import SamplingMetadata
 from vllm.v1.sample.rejection_sampler import (RejectionSampler,
                                               apply_sampling_constraints,
@@ -149,25 +150,36 @@ def rejection_sample(
     if not sampling_metadata.all_random:
         # Rejection sampling for greedy sampling requests.
         target_argmax = target_probs.argmax(dim=-1)
-        if min(num_draft_tokens) == 1 and max(
-                num_draft_tokens) == 1 and sampling_metadata.all_greedy:
-            rejection_greedy_sample_spec_len_1_pytorch(
-                output_token_ids,
-                draft_token_ids,
-                target_argmax,
-                bonus_token_ids,
-            )
-        else:
-            rejection_greedy_sample_pytorch(
+        if HAS_TRITON:
+            rejection_greedy_sample_kernel[(batch_size, )](
                 output_token_ids,
                 cu_num_draft_tokens,
                 draft_token_ids,
                 target_argmax,
                 bonus_token_ids,
-                num_draft_tokens,
-                max_spec_len,
                 is_greedy,
+                max_spec_len,
             )
+        else:
+            if min(num_draft_tokens) == 1 and max(
+                    num_draft_tokens) == 1 and sampling_metadata.all_greedy:
+                rejection_greedy_sample_spec_len_1_pytorch(
+                    output_token_ids,
+                    draft_token_ids,
+                    target_argmax,
+                    bonus_token_ids,
+                )
+            else:
+                rejection_greedy_sample_pytorch(
+                    output_token_ids,
+                    cu_num_draft_tokens,
+                    draft_token_ids,
+                    target_argmax,
+                    bonus_token_ids,
+                    num_draft_tokens,
+                    max_spec_len,
+                    is_greedy,
+                )
         if sampling_metadata.all_greedy:
             return output_token_ids
 
@@ -194,21 +206,37 @@ def rejection_sample(
     )
 
     # Rejection sampling for random sampling requests.
-    rejection_random_sample_pytorch(
-        output_token_ids,
-        cu_num_draft_tokens,
-        draft_token_ids,
-        draft_probs,
-        target_probs,
-        bonus_token_ids,
-        recovered_token_ids,
-        uniform_probs,
-        is_greedy,
-        max_spec_len,
-        vocab_size,
-        IS_NGRAM=draft_probs is None,
-        # num_warps=1,
-    )
+    if HAS_TRITON:
+        rejection_random_sample_kernel[(batch_size, )](
+            output_token_ids,
+            cu_num_draft_tokens,
+            draft_token_ids,
+            draft_probs,
+            target_probs,
+            bonus_token_ids,
+            recovered_token_ids,
+            uniform_probs,
+            is_greedy,
+            max_spec_len,
+            vocab_size,
+            NO_DRAFT_PROBS=draft_probs is None,
+        )
+    else:
+        rejection_random_sample_pytorch(
+            output_token_ids,
+            cu_num_draft_tokens,
+            draft_token_ids,
+            draft_probs,
+            target_probs,
+            bonus_token_ids,
+            recovered_token_ids,
+            uniform_probs,
+            is_greedy,
+            max_spec_len,
+            vocab_size,
+            IS_NGRAM=draft_probs is None,
+            # num_warps=1,
+        )
     return output_token_ids
 
 
@@ -241,14 +269,24 @@ def expand_batch_to_tokens(
     batch_size = x.shape[0]
     assert cu_num_tokens.shape[0] == batch_size
     expanded_x = x.new_empty(num_tokens)
-    expand_pytorch(
-        expanded_x,
-        x,
-        cu_num_tokens,
-        replace_from,
-        replace_to,
-        MAX_NUM_TOKENS=MAX_SPEC_LEN,  # To avoid recompilation.
-    )
+    if HAS_TRITON:
+        expand_kernel[(batch_size, )](
+            expanded_x,
+            x,
+            cu_num_tokens,
+            replace_from,
+            replace_to,
+            MAX_NUM_TOKENS=MAX_SPEC_LEN,  # To avoid recompilation.
+        )
+    else:
+        expand_pytorch(
+            expanded_x,
+            x,
+            cu_num_tokens,
+            replace_from,
+            replace_to,
+            MAX_NUM_TOKENS=MAX_SPEC_LEN,  # To avoid recompilation.
+        )
     return expanded_x
 
 
@@ -282,16 +320,29 @@ def sample_recovered_tokens(
             q[i].exponential_(generator=generator)
 
     recovered_token_ids = torch.empty_like(draft_token_ids)
-    sample_recovered_tokens_pytorch(
-        recovered_token_ids,
-        cu_num_draft_tokens,
-        draft_token_ids,
-        draft_probs,
-        target_probs,
-        q,
-        vocab_size,
-        IS_NGRAM=draft_probs is None,
-    )
+    if HAS_TRITON:
+        sample_recovered_tokens_kernel[(batch_size, max_spec_len)](
+            recovered_token_ids,
+            cu_num_draft_tokens,
+            draft_token_ids,
+            draft_probs,
+            target_probs,
+            q,
+            vocab_size,
+            triton.next_power_of_2(vocab_size),
+            NO_DRAFT_PROBS=draft_probs is None,
+        )
+    else:
+        sample_recovered_tokens_pytorch(
+            recovered_token_ids,
+            cu_num_draft_tokens,
+            draft_token_ids,
+            draft_probs,
+            target_probs,
+            q,
+            vocab_size,
+            IS_NGRAM=draft_probs is None,
+        )
     return recovered_token_ids
 
 
@@ -504,4 +555,192 @@ def sample_recovered_tokens_pytorch(
                 target_probs[token_idx, draft_token_id] = orig_prob
 
 
+@triton.jit(do_not_specialize=["max_spec_len"])
+def rejection_greedy_sample_kernel(
+    output_token_ids_ptr,  # [batch_size, max_spec_len + 1]
+    cu_num_draft_tokens_ptr,  # [batch_size]
+    draft_token_ids_ptr,  # [num_tokens]
+    target_argmax_ptr,  # [num_tokens]
+    bonus_token_ids_ptr,  # [batch_size]
+    is_greedy_ptr,  # [batch_size] or None
+    max_spec_len,
+):
+    req_idx = tl.program_id(0)
+    # Because is_greedy_ptr is not Nonr at profiling run,
+    # re-comilation may happen during runtime when is_greedy_ptr is None.
+    is_greedy = True if is_greedy_ptr is None else tl.load(is_greedy_ptr +
+                                                           req_idx)
+    if not is_greedy:
+        # Early exit for non-greedy sampling requests
+        return
+
+    start_idx = 0 if req_idx == 0 else tl.load(cu_num_draft_tokens_ptr +
+                                               req_idx - 1)
+    end_idx = tl.load(cu_num_draft_tokens_ptr + req_idx)
+    num_draft_tokens = end_idx - start_idx
+
+    rejected = False
+    for pos in range(num_draft_tokens):
+        if not rejected:
+            draft_token_id = tl.load(draft_token_ids_ptr + start_idx + pos)
+            target_argmax_id = tl.load(target_argmax_ptr + start_idx + pos)
+            tl.store(
+                output_token_ids_ptr + req_idx * (max_spec_len + 1) + pos,
+                target_argmax_id,
+            )
+            if draft_token_id != target_argmax_id:
+                # Reject
+                rejected = True
+
+    if not rejected:
+        # If all tokens are accepted, append the bonus token
+        bonus_token_id = tl.load(bonus_token_ids_ptr + req_idx)
+        tl.store(
+            output_token_ids_ptr + req_idx * (max_spec_len + 1) +
+            num_draft_tokens,
+            bonus_token_id,
+        )
+
+
+@triton.jit(do_not_specialize=["max_spec_len"])
+def rejection_random_sample_kernel(
+    output_token_ids_ptr,  # [batch_size, max_spec_len + 1]
+    cu_num_draft_tokens_ptr,  # [batch_size]
+    draft_token_ids_ptr,  # [num_tokens]
+    draft_probs_ptr,  # [num_tokens, vocab_size] or None
+    target_probs_ptr,  # [num_tokens, vocab_size]
+    bonus_token_ids_ptr,  # [batch_size]
+    recovered_token_ids_ptr,  # [num_tokens]
+    uniform_probs_ptr,  # [num_tokens]
+    is_greedy_ptr,  # [batch_size]
+    max_spec_len,
+    vocab_size,
+    NO_DRAFT_PROBS: tl.constexpr,
+):
+    req_idx = tl.program_id(0)
+    is_greedy = tl.load(is_greedy_ptr + req_idx)
+    if is_greedy:
+        # Early exost for greedy sampling requests
+        return
+
+    start_idx = 0 if req_idx == 0 else tl.load(cu_num_draft_tokens_ptr +
+                                               req_idx - 1)
+    end_idx = tl.load(cu_num_draft_tokens_ptr + req_idx)
+    num_draft_tokens = end_idx - start_idx
+
+    rejected = False
+    for pos in range(num_draft_tokens):
+        if not rejected:
+            draft_token_id = tl.load(draft_token_ids_ptr + start_idx + pos)
+            if NO_DRAFT_PROBS:
+                draft_prob = 1
+            else:
+                draft_prob = tl.load(draft_probs_ptr +
+                                     (start_idx + pos) * vocab_size +
+                                     draft_token_id)
+            target_prob = tl.load(target_probs_ptr +
+                                  (start_idx + pos) * vocab_size +
+                                  draft_token_id)
+            uniform_prob = tl.load(uniform_probs_ptr + start_idx + pos)
+            if draft_prob > 0 and target_prob / draft_prob >= uniform_prob:
+                # Accept
+                token_id = draft_token_id
+            else:
+                # Reject. Use recovered token
+                rejected = True
+                token_id = tl.load(recovered_token_ids_ptr + start_idx + pos)
+            tl.store(output_token_ids_ptr + req_idx * (max_spec_len + 1) + pos,
+                     token_id)
+
+    if not rejected:
+        # If all tokens are accepted, append the bonus token
+        bonus_token_id = tl.load(bonus_token_ids_ptr + req_idx)
+        tl.store(
+            output_token_ids_ptr + req_idx * (max_spec_len + 1) +
+            num_draft_tokens,
+            bonus_token_id,
+        )
+
+
+@triton.jit(do_not_specialize=["replace_from", "replace_to"])
+def expand_kernel(
+    output_ptr,  # [num_tokens]
+    input_ptr,  # [batch_size]
+    cu_num_tokens_ptr,  # [batch_size]
+    replace_from,
+    replace_to,
+    MAX_NUM_TOKENS: tl.constexpr,
+):
+    req_idx = tl.program_id(0)
+    if req_idx == 0:
+        start_idx = 0
+    else:
+        start_idx = tl.load(cu_num_tokens_ptr + req_idx - 1)
+    end_idx = tl.load(cu_num_tokens_ptr + req_idx)
+    num_tokens = end_idx - start_idx
+
+    src_val = tl.load(input_ptr + req_idx)
+    src_val = tl.where(src_val == replace_from, replace_to, src_val)
+    offset = tl.arange(0, MAX_NUM_TOKENS)
+    tl.store(output_ptr + start_idx + offset,
+             src_val,
+             mask=offset < num_tokens)
+
+
+@triton.jit
+def sample_recovered_tokens_kernel(
+    output_token_ids_ptr,  # [num_tokens]
+    cu_num_draft_tokens_ptr,  # [batch_size]
+    draft_token_ids_ptr,  # [num_tokens]
+    draft_probs_ptr,  # [num_tokens, vocab_size] or None
+    target_probs_ptr,  # [num_tokens, vocab_size]
+    q_ptr,  # [batch_size, vocab_size]
+    vocab_size,
+    PADDED_VOCAB_SIZE: tl.constexpr,
+    NO_DRAFT_PROBS: tl.constexpr,
+):
+    req_idx = tl.program_id(0)
+    start_idx = 0 if req_idx == 0 else tl.load(cu_num_draft_tokens_ptr +
+                                               req_idx - 1)
+    end_idx = tl.load(cu_num_draft_tokens_ptr + req_idx)
+    num_draft_tokens = end_idx - start_idx
+
+    # Early exit for out-of-range positions
+    pos = tl.program_id(1)
+    if pos >= num_draft_tokens:
+        return
+
+    vocab_offset = tl.arange(0, PADDED_VOCAB_SIZE)
+    if NO_DRAFT_PROBS:
+        draft_token_id = tl.load(draft_token_ids_ptr + start_idx + pos)
+        prob = tl.load(
+            target_probs_ptr + (start_idx + pos) * vocab_size + vocab_offset,
+            mask=((vocab_offset < vocab_size) &
+                  (vocab_offset != draft_token_id)),
+            other=0,
+        )
+    else:
+        draft_prob = tl.load(
+            draft_probs_ptr + (start_idx + pos) * vocab_size + vocab_offset,
+            mask=vocab_offset < vocab_size,
+            other=0,
+        )
+        target_prob = tl.load(
+            target_probs_ptr + (start_idx + pos) * vocab_size + vocab_offset,
+            mask=vocab_offset < vocab_size,
+            other=0,
+        )
+        prob = tl.maximum(target_prob - draft_prob, 0)
+        # We don't need `prob = prob / tl.sum(prob)` here because
+        # `tl.argmax` will select the maximum value.
+
+    q = tl.load(
+        q_ptr + req_idx * vocab_size + vocab_offset,
+        mask=vocab_offset < vocab_size,
+        other=float("-inf"),
+    )
+    recovered_id = tl.argmax(prob / q, axis=-1)
+    tl.store(output_token_ids_ptr + start_idx + pos, recovered_id)
+
+
 rs.expand_batch_to_tokens = expand_batch_to_tokens