refactor: 抽离 runner 侧 KV compression 逻辑并统一 slot mapping

vllm/v1/kv_compression/runner_buffers.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from __future__ import annotations
+
+from typing import Any, Optional
+
+import torch
+
+
+def init_kv_compression_runner_buffers(
+    *,
+    runner: Any,
+    max_num_tokens: int,
+    max_num_reqs: int,
+    device: torch.device,
+    pin_memory: bool,
+) -> None:
+    """Initialize per-runner buffers used by KV compression.
+
+    This helper keeps `gpu_model_runner.py` focused on orchestration while
+    preserving the existing attribute-based access patterns.
+    """
+    # KV positions are decoupled from logical positions when KV compression is
+    # enabled. Keep a separate buffer to avoid recomputing or overwriting the
+    # logical `positions_np` (used for RoPE / token lookup).
+    runner.kv_positions_cpu = torch.zeros(
+        max_num_tokens,
+        dtype=torch.int64,
+        device="cpu",
+        pin_memory=pin_memory,
+    )
+    runner.kv_positions_np = runner.kv_positions_cpu.numpy()
+
+    # KV compression metadata buffers (used by the "topk" policy).
+    # Per-token: whether this scheduled token must be kept in KV cache.
+    runner.kv_compression_must_keep_cpu = torch.zeros(
+        max_num_tokens,
+        dtype=torch.bool,
+        device="cpu",
+        pin_memory=pin_memory,
+    )
+    runner.kv_compression_must_keep_np = runner.kv_compression_must_keep_cpu.numpy()
+    runner.kv_compression_must_keep = torch.zeros(
+        max_num_tokens,
+        dtype=torch.bool,
+        device=device,
+    )
+
+    # Per-request: how many additional prompt tokens to keep among
+    # non-protected candidates (budget from env; selection uses scores).
+    runner.kv_compression_topk_budget_cpu = torch.zeros(
+        max_num_reqs,
+        dtype=torch.int32,
+        device="cpu",
+        pin_memory=pin_memory,
+    )
+    runner.kv_compression_topk_budget_np = runner.kv_compression_topk_budget_cpu.numpy()
+    runner.kv_compression_topk_budget = torch.zeros(
+        max_num_reqs,
+        dtype=torch.int32,
+        device=device,
+    )
+
+    # Chunked-prefill prompt-end KV compression metadata (scheme 3).
+    # Per-request: whether this step finishes the prompt and should compute
+    # global prompt indices (score/topk) for a one-shot compaction.
+    runner.kv_compression_prompt_end_cpu = torch.zeros(
+        max_num_reqs,
+        dtype=torch.bool,
+        device="cpu",
+        pin_memory=pin_memory,
+    )
+    runner.kv_compression_prompt_end_np = runner.kv_compression_prompt_end_cpu.numpy()
+    runner.kv_compression_prompt_end = torch.zeros(
+        max_num_reqs,
+        dtype=torch.bool,
+        device=device,
+    )
+
+    # Per-request: prompt length (tokens) and Top-K keep count among prompt
+    # candidates (excluding protected prefix/suffix).
+    runner.kv_compression_prompt_lens_cpu = torch.zeros(
+        max_num_reqs,
+        dtype=torch.int32,
+        device="cpu",
+        pin_memory=pin_memory,
+    )
+    runner.kv_compression_prompt_lens_np = runner.kv_compression_prompt_lens_cpu.numpy()
+    runner.kv_compression_prompt_lens = torch.zeros(
+        max_num_reqs,
+        dtype=torch.int32,
+        device=device,
+    )
+
+    runner.kv_compression_prompt_topk_keep_cpu = torch.zeros(
+        max_num_reqs,
+        dtype=torch.int32,
+        device="cpu",
+        pin_memory=pin_memory,
+    )
+    runner.kv_compression_prompt_topk_keep_np = runner.kv_compression_prompt_topk_keep_cpu.numpy()
+    runner.kv_compression_prompt_topk_keep = torch.zeros(
+        max_num_reqs,
+        dtype=torch.int32,
+        device=device,
+    )
+    runner.kv_compression_prompt_topk_keep_max = None  # type: Optional[int]
+

vllm/v1/kv_compression/runner_prepare.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from __future__ import annotations
+
+from typing import Optional
+
+import numpy as np
+
+import vllm.envs as envs
+from vllm.v1.kv_compression.budget import (compute_prompt_topk_keep_total,
+                                           compute_topk_budget_step)
+
+
+def prepare_kv_compression_for_step(
+    *,
+    num_reqs: int,
+    total_num_scheduled_tokens: int,
+    num_scheduled_tokens: np.ndarray,  # [B] int32
+    cu_num_tokens: np.ndarray,  # [B] int64/int32 cumulative scheduled tokens
+    req_indices: np.ndarray,  # [T] int64, request index per token
+    arange: np.ndarray,  # [T] int64, position-within-request per token
+    num_computed_tokens_cpu: np.ndarray,  # [max_reqs] int32/int64
+    num_prompt_tokens: np.ndarray,  # [max_reqs] int32/int64
+    num_kv_tokens_cpu: np.ndarray,  # [max_reqs] int32/int64
+    kv_positions_np: np.ndarray,  # [T] int64 (out)
+    must_keep_np: np.ndarray,  # [T] bool (out; scheme 1/2 only)
+    topk_budget_np: np.ndarray,  # [B] int32 (out; scheme 1/2 only)
+    prompt_end_np: np.ndarray,  # [B] bool (out; scheme 3 only)
+    prompt_lens_np: np.ndarray,  # [B] int32 (out; scheme 3 only)
+    prompt_topk_keep_np: np.ndarray,  # [B] int32 (out; scheme 3 only)
+    chunked_prefill_enabled: bool,
+) -> tuple[bool, Optional[int]]:
+    """Prepare KV compression metadata for a single model step (CPU-side).
+
+    Fills:
+    - `kv_positions_np`: per-token KV write positions (decoupled from logical
+      RoPE positions).
+    - Scheme 3 (chunked prefill): `prompt_end/prompt_lens/prompt_topk_keep`.
+    - Scheme 1/2 (non-chunked): `must_keep/topk_budget`.
+
+    Returns:
+      (needs_compaction, prompt_topk_keep_max)
+    """
+    if total_num_scheduled_tokens <= 0 or num_reqs <= 0:
+        return False, None
+
+    # KV positions (where scheduled tokens are written before optional
+    # compaction).
+    np.add(num_kv_tokens_cpu[req_indices], arange, out=kv_positions_np)
+
+    prompt_ratio = envs.VLLM_KV_COMPRESSION_PROMPT_RATIO
+    prompt_budget = envs.VLLM_KV_COMPRESSION_PROMPT_BUDGET
+    protected_prefix = envs.VLLM_KV_COMPRESSION_PROTECTED_PREFIX
+    protected_suffix = envs.VLLM_KV_COMPRESSION_PROTECTED_SUFFIX
+    keep_last = envs.VLLM_KV_COMPRESSION_KEEP_LAST_TOKEN
+
+    if chunked_prefill_enabled:
+        # Scheme 3: with chunked prefill, defer compaction until after the full
+        # prompt is ingested. Otherwise, the next prefill chunk would attend to
+        # a truncated history and quality can collapse.
+        prompt_end_np.fill(False)
+        prompt_lens_np.fill(0)
+        prompt_topk_keep_np.fill(0)
+
+        for req_idx in range(num_reqs):
+            qlen = int(num_scheduled_tokens[req_idx])
+            if qlen <= 0:
+                continue
+            base_pos = int(num_computed_tokens_cpu[req_idx])
+            prompt_len = int(num_prompt_tokens[req_idx])
+            end_pos = base_pos + qlen
+            ends_prompt = (base_pos < prompt_len) and (end_pos >= prompt_len)
+            if not ends_prompt:
+                continue
+
+            prompt_end_np[req_idx] = True
+            prompt_lens_np[req_idx] = prompt_len
+            prompt_topk_keep_np[req_idx] = compute_prompt_topk_keep_total(
+                prompt_len=prompt_len,
+                protected_prefix=protected_prefix,
+                protected_suffix=protected_suffix,
+                keep_last_token=keep_last,
+                prompt_ratio=prompt_ratio,
+                prompt_budget=prompt_budget,
+            )
+
+        prompt_topk_keep_max = int(prompt_topk_keep_np[:num_reqs].max())
+        return False, prompt_topk_keep_max
+
+    # Scheme 1/2: per-step compaction within the scheduled segment.
+    must_keep_np.fill(False)
+    topk_budget_np.fill(0)
+
+    for req_idx in range(num_reqs):
+        qlen = int(num_scheduled_tokens[req_idx])
+        if qlen <= 0:
+            continue
+        start = 0 if req_idx == 0 else int(cu_num_tokens[req_idx - 1])
+        end = int(cu_num_tokens[req_idx])
+        assert end - start == qlen
+
+        base_pos = int(num_computed_tokens_cpu[req_idx])
+        prompt_len = int(num_prompt_tokens[req_idx])
+        end_pos = base_pos + qlen
+        pos_in_req = arange[start:end].astype(np.int64, copy=False)
+        pos = base_pos + pos_in_req
+
+        prompt_mask = pos < prompt_len
+        # Decode tokens are always kept.
+        must_keep = ~prompt_mask
+
+        if np.any(prompt_mask):
+            suffix_start = max(prompt_len - protected_suffix, 0)
+            must_keep |= prompt_mask & (pos < protected_prefix)
+            must_keep |= prompt_mask & (pos >= suffix_start)
+            if keep_last:
+                last = prompt_len - 1
+                if base_pos <= last < end_pos:
+                    must_keep[last - base_pos] = True
+
+            topk_budget_np[req_idx] = compute_topk_budget_step(
+                prompt_len=prompt_len,
+                start_pos=base_pos,
+                end_pos=end_pos,
+                protected_prefix=protected_prefix,
+                protected_suffix=protected_suffix,
+                keep_last_token=keep_last,
+                prompt_ratio=prompt_ratio,
+                prompt_budget=prompt_budget,
+            )
+
+        must_keep_np[start:end] = must_keep
+
+    # Decode-only fast path: if all scheduled tokens are unconditionally kept
+    # and there is no Top-K budget, KV compaction is a no-op and can be skipped.
+    needs_compaction = (not must_keep_np.all()) or (topk_budget_np > 0).any()
+    return bool(needs_compaction), None
+

vllm/v1/kv_compression/runner_prompt_compaction.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from __future__ import annotations
+
+from typing import Any
+
+import torch
+
+import vllm.envs as envs
+from vllm.forward_context import get_forward_context
+from vllm.platforms import current_platform
+from vllm.v1.kv_compression.forward_context import get_kv_compression_prompt_payload
+
+
+def stash_kv_compression_prompt_payload_to_requests(*, runner: Any) -> None:
+    """Persist prompt-end compaction indices from the forward context.
+
+    This is the runner-side half of chunked-prefill scheme 3:
+      flash_attn -> forward_context payload -> request state stash ->
+      (next step) one-shot KV compaction.
+    """
+    if not envs.VLLM_ENABLE_KV_COMPRESSION:
+        return
+    scheduler_config = getattr(runner, "scheduler_config", None)
+    if scheduler_config is None or not getattr(scheduler_config,
+                                              "chunked_prefill_enabled",
+                                              False):
+        return
+
+    forward_context = get_forward_context()
+    payload = get_kv_compression_prompt_payload(forward_context)
+    if payload is None:
+        return
+
+    req_indices = payload.get("req_indices")
+    idx_sorted = payload.get("idx_sorted")
+    keep_len = payload.get("keep_len")
+    prompt_lens = payload.get("prompt_lens")
+    if (req_indices is None or idx_sorted is None or keep_len is None
+            or prompt_lens is None):
+        return
+
+    input_batch = getattr(runner, "input_batch", None)
+    if input_batch is None:
+        return
+    req_ids = getattr(input_batch, "req_ids", None)
+    if req_ids is None:
+        return
+    requests = getattr(runner, "requests", None)
+    if requests is None:
+        return
+
+    req_indices_cpu = req_indices.to(device="cpu", dtype=torch.int64).tolist()
+    keep_cpu = keep_len.to(device="cpu", dtype=torch.int64).tolist()
+    prompt_cpu = prompt_lens.to(device="cpu", dtype=torch.int64).tolist()
+    for i, b in enumerate(req_indices_cpu):
+        if b < 0 or b >= len(req_ids):
+            continue
+        req_id = req_ids[b]
+        if req_id is None:
+            continue
+        rs = requests.get(req_id)
+        if rs is None:
+            continue
+        rs.kv_compression_prompt_idx_sorted = idx_sorted[i]
+        rs.kv_compression_prompt_keep_len = int(keep_cpu[i])
+        rs.kv_compression_prompt_prompt_len = int(prompt_cpu[i])
+
+
+def maybe_apply_kv_compression_prompt_compaction(*, runner: Any) -> None:
+    """Apply one-shot prompt KV compaction before the first decode step."""
+    if not envs.VLLM_ENABLE_KV_COMPRESSION:
+        return
+    scheduler_config = getattr(runner, "scheduler_config", None)
+    if scheduler_config is None or not getattr(scheduler_config,
+                                              "chunked_prefill_enabled",
+                                              False):
+        return
+
+    input_batch = getattr(runner, "input_batch", None)
+    if input_batch is None:
+        return
+    requests = getattr(runner, "requests", None)
+    if requests is None:
+        return
+
+    pending_req_ids: list[str] = []
+    for req_id in input_batch.req_ids:
+        if req_id is None:
+            continue
+        rs = requests.get(req_id)
+        if rs is None:
+            continue
+        if rs.kv_compression_prompt_idx_sorted is None:
+            continue
+        # Only apply once the prompt is fully ingested (decode stage).
+        if rs.num_computed_tokens < rs.num_prompt_tokens:
+            continue
+        pending_req_ids.append(req_id)
+
+    if not pending_req_ids:
+        return
+
+    device = runner.device
+    pending_states: list[tuple[str, torch.Tensor, int]] = []
+    for req_id in pending_req_ids:
+        rs = requests[req_id]
+        keep = rs.kv_compression_prompt_keep_len
+        idx = rs.kv_compression_prompt_idx_sorted
+        if keep is None or idx is None:
+            continue
+        keep_i = int(keep)
+        if keep_i <= 0:
+            # No prompt tokens kept; clear and skip.
+            rs.kv_compression_prompt_idx_sorted = None
+            rs.kv_compression_prompt_keep_len = None
+            rs.kv_compression_prompt_prompt_len = None
+            continue
+        pending_states.append((req_id, idx, keep_i))
+
+    if not pending_states:
+        return
+
+    B = len(pending_states)
+    keep_list = [k for _, _, k in pending_states]
+    K_max = max(keep_list)
+    idx_batch = torch.zeros((B, K_max), device=device, dtype=torch.int32)
+    for i, (_, row, k) in enumerate(pending_states):
+        idx_batch[i, :k] = row[:k].to(device=device, dtype=torch.int32)
+    keep_tensor = torch.tensor(keep_list, device=device, dtype=torch.int32)
+
+    from vllm.v1.kv_compression.kv_cache_triton import (
+        front_compact_inplace_fa_triton, make_fa_cache_view)
+
+    kv_cache_config = getattr(runner, "kv_cache_config", None)
+    if kv_cache_config is None:
+        return
+
+    # Apply compaction to every attention layer's KV cache in-place.
+    for group_id, kv_cache_group_spec in enumerate(
+            kv_cache_config.kv_cache_groups):
+        max_blocks = 0
+        for req_id, _, _ in pending_states:
+            rs = requests[req_id]
+            if group_id >= len(rs.block_ids):
+                continue
+            max_blocks = max(max_blocks, len(rs.block_ids[group_id]))
+        if max_blocks == 0:
+            continue
+
+        block_table_cpu = torch.zeros((B, max_blocks),
+                                      dtype=torch.int32,
+                                      device="cpu")
+        for i, (req_id, _, _) in enumerate(pending_states):
+            rs = requests[req_id]
+            if group_id >= len(rs.block_ids):
+                continue
+            ids = rs.block_ids[group_id]
+            if ids:
+                block_table_cpu[i, :len(ids)] = torch.tensor(ids,
+                                                            dtype=torch.int32,
+                                                            device="cpu")
+        block_table = block_table_cpu.to(device=device, non_blocking=True)
+
+        kv_caches = getattr(runner, "kv_caches", None)
+        if kv_caches is None:
+            continue
+
+        for layer_name in kv_cache_group_spec.layer_names:
+            layer_index = runner._extract_layer_index(layer_name)
+            if layer_index >= len(kv_caches):
+                continue
+            kv_cache = kv_caches[layer_index]
+            if not current_platform.is_rocm():
+                if not isinstance(kv_cache, torch.Tensor):
+                    continue
+                key_cache, value_cache = kv_cache.unbind(0)
+            else:
+                if (not isinstance(kv_cache, (tuple, list))
+                        or len(kv_cache) != 2):
+                    continue
+                key_cache, value_cache = kv_cache
+            k_view, v_view = make_fa_cache_view(key_cache=key_cache,
+                                                value_cache=value_cache)
+            front_compact_inplace_fa_triton(
+                k_view,
+                v_view,
+                block_table,
+                idx_batch,
+                keep_tensor,
+            )
+
+    # Clear pending state after successful compaction.
+    for req_id, _, _ in pending_states:
+        rs = requests.get(req_id)
+        if rs is None:
+            continue
+        rs.kv_compression_prompt_idx_sorted = None
+        rs.kv_compression_prompt_keep_len = None
+        rs.kv_compression_prompt_prompt_len = None

vllm/v1/kv_compression/runner_step.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from __future__ import annotations
+
+from typing import Any, Optional
+
+import numpy as np
+
+import vllm.envs as envs
+
+from vllm.v1.kv_compression.runner_prepare import prepare_kv_compression_for_step
+
+
+def maybe_prepare_kv_compression_for_runner_step(
+    *,
+    runner: Any,
+    num_reqs: int,
+    total_num_scheduled_tokens: int,
+    num_scheduled_tokens: np.ndarray,  # [B] int32
+    cu_num_tokens: np.ndarray,  # [B] int64/int32
+    req_indices: np.ndarray,  # [T] int64
+    arange: np.ndarray,  # [T] int64
+) -> Optional[np.ndarray]:
+    """Prepare per-step KV compression metadata on CPU.
+
+    Returns the per-token KV positions (`kv_positions_np`) or None if KV
+    compression is disabled.
+    """
+    if not envs.VLLM_ENABLE_KV_COMPRESSION:
+        runner.kv_compression_needs_compaction = False
+        return None
+
+    kv_positions_np = runner.kv_positions_np[:total_num_scheduled_tokens]
+    must_keep_np = runner.kv_compression_must_keep_np[:total_num_scheduled_tokens]
+    topk_budget_np = runner.kv_compression_topk_budget_np[:num_reqs]
+    prompt_end_np = runner.kv_compression_prompt_end_np[:num_reqs]
+    prompt_lens_np = runner.kv_compression_prompt_lens_np[:num_reqs]
+    topk_keep_np = runner.kv_compression_prompt_topk_keep_np[:num_reqs]
+
+    needs_compaction, prompt_topk_keep_max = prepare_kv_compression_for_step(
+        num_reqs=num_reqs,
+        total_num_scheduled_tokens=total_num_scheduled_tokens,
+        num_scheduled_tokens=num_scheduled_tokens,
+        cu_num_tokens=cu_num_tokens,
+        req_indices=req_indices,
+        arange=arange,
+        num_computed_tokens_cpu=runner.input_batch.num_computed_tokens_cpu,
+        num_prompt_tokens=runner.input_batch.num_prompt_tokens,
+        num_kv_tokens_cpu=runner.input_batch.num_kv_tokens_cpu,
+        kv_positions_np=kv_positions_np,
+        must_keep_np=must_keep_np,
+        topk_budget_np=topk_budget_np,
+        prompt_end_np=prompt_end_np,
+        prompt_lens_np=prompt_lens_np,
+        prompt_topk_keep_np=topk_keep_np,
+        chunked_prefill_enabled=runner.scheduler_config.chunked_prefill_enabled,
+    )
+    runner.kv_compression_needs_compaction = bool(needs_compaction)
+    if prompt_topk_keep_max is not None:
+        runner.kv_compression_prompt_topk_keep_max = int(prompt_topk_keep_max)
+    return kv_positions_np
+
+
+def maybe_copy_kv_compression_step_tensors_to_gpu(
+    *,
+    runner: Any,
+    num_reqs: int,
+    total_num_scheduled_tokens: int,
+    non_blocking: bool = True,
+) -> None:
+    """Stage per-step KV compression tensors to GPU if needed."""
+    if not envs.VLLM_ENABLE_KV_COMPRESSION:
+        return
+
+    if runner.scheduler_config.chunked_prefill_enabled:
+        runner.kv_compression_prompt_end[:num_reqs].copy_(
+            runner.kv_compression_prompt_end_cpu[:num_reqs],
+            non_blocking=non_blocking,
+        )
+        runner.kv_compression_prompt_lens[:num_reqs].copy_(
+            runner.kv_compression_prompt_lens_cpu[:num_reqs],
+            non_blocking=non_blocking,
+        )
+        runner.kv_compression_prompt_topk_keep[:num_reqs].copy_(
+            runner.kv_compression_prompt_topk_keep_cpu[:num_reqs],
+            non_blocking=non_blocking,
+        )
+        return
+
+    if runner.kv_compression_needs_compaction:
+        runner.kv_compression_must_keep[:total_num_scheduled_tokens].copy_(
+            runner.kv_compression_must_keep_cpu[:total_num_scheduled_tokens],
+            non_blocking=non_blocking,
+        )
+        runner.kv_compression_topk_budget[:num_reqs].copy_(
+            runner.kv_compression_topk_budget_cpu[:num_reqs],
+            non_blocking=non_blocking,
+        )
+

vllm/v1/worker/gpu_model_runner.py

@@ -55,8 +55,15 @@ from vllm.v1.core.encoder_cache_manager import compute_encoder_budget
 from vllm.v1.kv_cache_interface import (AttentionSpec, FullAttentionSpec,
                                         KVCacheConfig, KVCacheSpec, MambaSpec,
                                         SlidingWindowSpec)
-from vllm.v1.kv_compression.budget import (compute_prompt_topk_keep_total,
-                                           compute_topk_budget_step)
+from vllm.v1.kv_compression.runner_buffers import init_kv_compression_runner_buffers
+from vllm.v1.kv_compression.runner_prompt_compaction import (
+    maybe_apply_kv_compression_prompt_compaction,
+    stash_kv_compression_prompt_payload_to_requests,
+)
+from vllm.v1.kv_compression.runner_step import (
+    maybe_copy_kv_compression_step_tensors_to_gpu,
+    maybe_prepare_kv_compression_for_runner_step,
+)
 from vllm.v1.outputs import (EMPTY_MODEL_RUNNER_OUTPUT, LogprobsTensors,
                              ModelRunnerOutput)
 from vllm.v1.pool.metadata import PoolingMetadata
@@ -72,12 +79,12 @@ from vllm.v1.utils import bind_kv_cache
 from vllm.v1.worker.block_table import BlockTable
 from vllm.v1.worker.gpu_input_batch import CachedRequestState, InputBatch
 from vllm.v1.worker.lora_model_runner_mixin import LoRAModelRunnerMixin
-from vllm.platforms import current_platform
 from vllm.two_batch_overlap.v1.model_input_split_v1 import tbo_split_and_execute_model
 from vllm.profiler.prof import profile
 from ..sample.logits_processor import LogitsProcessorManager
 from .utils import (gather_mm_placeholders, initialize_kv_cache_for_kv_sharing,
                     sanity_check_mm_encoder_outputs, scatter_mm_placeholders)
+from .slot_mapping_utils import fill_block_table_slot_mapping_np
 from vllm.zero_overhead.v1.eagle import V1ZeroEagleProposer
 from vllm.v1.spec_decode.utils import DraftProbs
 
@@ -322,14 +329,15 @@ class GPUModelRunnerBase(LoRAModelRunnerMixin):
                                          device="cpu",
                                          pin_memory=self.pin_memory)
         self.positions_np = self.positions_cpu.numpy()
-        # KV positions are decoupled from logical positions when KV compression
-        # is enabled. We keep a separate buffer to avoid recomputing or
-        # overwriting `positions_np` (used for RoPE / input token lookup).
-        self.kv_positions_cpu = torch.zeros(self.max_num_tokens,
-                                            dtype=torch.int64,
-                                            device="cpu",
-                                            pin_memory=self.pin_memory)
-        self.kv_positions_np = self.kv_positions_cpu.numpy()
+
+        init_kv_compression_runner_buffers(
+            runner=self,
+            max_num_tokens=self.max_num_tokens,
+            max_num_reqs=self.max_num_reqs,
+            device=self.device,
+            pin_memory=self.pin_memory,
+        )
+
         self.query_start_loc_cpu = torch.zeros(self.max_num_reqs + 1,
                                                dtype=torch.int32,
                                                device="cpu",
@@ -340,77 +348,6 @@ class GPUModelRunnerBase(LoRAModelRunnerMixin):
                                         device="cpu",
                                         pin_memory=self.pin_memory)
         self.seq_lens_np = self.seq_lens_cpu.numpy()
-        # KV compression metadata buffers (used by the "topk" policy).
-        # Per-token: whether this scheduled token must be kept in KV cache.
-        self.kv_compression_must_keep_cpu = torch.zeros(
-            self.max_num_tokens,
-            dtype=torch.bool,
-            device="cpu",
-            pin_memory=self.pin_memory,
-        )
-        self.kv_compression_must_keep_np = self.kv_compression_must_keep_cpu.numpy()
-        self.kv_compression_must_keep = torch.zeros(
-            self.max_num_tokens,
-            dtype=torch.bool,
-            device=self.device,
-        )
-        # Per-request: how many additional prompt tokens to keep among
-        # non-protected candidates (budget from env; selection uses scores).
-        self.kv_compression_topk_budget_cpu = torch.zeros(
-            self.max_num_reqs,
-            dtype=torch.int32,
-            device="cpu",
-            pin_memory=self.pin_memory,
-        )
-        self.kv_compression_topk_budget_np = self.kv_compression_topk_budget_cpu.numpy()
-        self.kv_compression_topk_budget = torch.zeros(
-            self.max_num_reqs,
-            dtype=torch.int32,
-            device=self.device,
-        )
-
-        # Chunked-prefill prompt-end KV compression metadata (scheme 3).
-        # Per-request: whether this step finishes the prompt and should compute
-        # global prompt indices (score/topk) for a one-shot compaction.
-        self.kv_compression_prompt_end_cpu = torch.zeros(
-            self.max_num_reqs,
-            dtype=torch.bool,
-            device="cpu",
-            pin_memory=self.pin_memory,
-        )
-        self.kv_compression_prompt_end_np = self.kv_compression_prompt_end_cpu.numpy()
-        self.kv_compression_prompt_end = torch.zeros(
-            self.max_num_reqs,
-            dtype=torch.bool,
-            device=self.device,
-        )
-        # Per-request: prompt length (tokens) and Top-K keep count among prompt
-        # candidates (excluding protected prefix/suffix).
-        self.kv_compression_prompt_lens_cpu = torch.zeros(
-            self.max_num_reqs,
-            dtype=torch.int32,
-            device="cpu",
-            pin_memory=self.pin_memory,
-        )
-        self.kv_compression_prompt_lens_np = self.kv_compression_prompt_lens_cpu.numpy()
-        self.kv_compression_prompt_lens = torch.zeros(
-            self.max_num_reqs,
-            dtype=torch.int32,
-            device=self.device,
-        )
-        self.kv_compression_prompt_topk_keep_cpu = torch.zeros(
-            self.max_num_reqs,
-            dtype=torch.int32,
-            device="cpu",
-            pin_memory=self.pin_memory,
-        )
-        self.kv_compression_prompt_topk_keep_np = self.kv_compression_prompt_topk_keep_cpu.numpy()
-        self.kv_compression_prompt_topk_keep = torch.zeros(
-            self.max_num_reqs,
-            dtype=torch.int32,
-            device=self.device,
-        )
-        self.kv_compression_prompt_topk_keep_max: Optional[int] = None
 
         # Layer pairings for cross-layer KV sharing.
         # If an Attention layer `layer_name` is in the keys of this dict, it
@@ -779,110 +716,17 @@ class GPUModelRunnerBase(LoRAModelRunnerMixin):
         # from logical positions.
         use_kv_compression = envs.VLLM_ENABLE_KV_COMPRESSION
         if use_kv_compression:
-            kv_positions_np = self.kv_positions_np[:total_num_scheduled_tokens]
-            np.add(self.input_batch.num_kv_tokens_cpu[req_indices],
-                   arange,
-                   out=kv_positions_np)
-        else:
-            kv_positions_np = None
-
-        if use_kv_compression:
-            prompt_ratio = envs.VLLM_KV_COMPRESSION_PROMPT_RATIO
-            prompt_budget = envs.VLLM_KV_COMPRESSION_PROMPT_BUDGET
-            protected_prefix = envs.VLLM_KV_COMPRESSION_PROTECTED_PREFIX
-            protected_suffix = envs.VLLM_KV_COMPRESSION_PROTECTED_SUFFIX
-            keep_last = envs.VLLM_KV_COMPRESSION_KEEP_LAST_TOKEN
-
-            if self.scheduler_config.chunked_prefill_enabled:
-                # Scheme 3: with chunked prefill, defer compaction until after
-                # the full prompt is ingested. Otherwise, the next prefill chunk
-                # would attend to a truncated history and quality can collapse.
-                prompt_end_np = self.kv_compression_prompt_end_np[:num_reqs]
-                prompt_end_np.fill(False)
-                prompt_lens_np = self.kv_compression_prompt_lens_np[:num_reqs]
-                prompt_lens_np.fill(0)
-                topk_keep_np = self.kv_compression_prompt_topk_keep_np[:num_reqs]
-                topk_keep_np.fill(0)
-
-                for req_idx in range(num_reqs):
-                    qlen = int(num_scheduled_tokens[req_idx])
-                    if qlen <= 0:
-                        continue
-                    base_pos = int(self.input_batch.num_computed_tokens_cpu[req_idx])
-                    prompt_len = int(self.input_batch.num_prompt_tokens[req_idx])
-                    end_pos = base_pos + qlen
-                    ends_prompt = (base_pos < prompt_len) and (end_pos >= prompt_len)
-                    if not ends_prompt:
-                        continue
-
-                    prompt_end_np[req_idx] = True
-                    prompt_lens_np[req_idx] = prompt_len
-                    topk_keep_np[req_idx] = compute_prompt_topk_keep_total(
-                        prompt_len=prompt_len,
-                        protected_prefix=protected_prefix,
-                        protected_suffix=protected_suffix,
-                        keep_last_token=keep_last,
-                        prompt_ratio=prompt_ratio,
-                        prompt_budget=prompt_budget,
-                    )
-
-                self.kv_compression_prompt_topk_keep_max = int(
-                    topk_keep_np[:num_reqs].max()) if num_reqs > 0 else 0
-                self.kv_compression_needs_compaction = False
-            else:
-                must_keep_np = self.kv_compression_must_keep_np[
-                    :total_num_scheduled_tokens]
-                must_keep_np.fill(False)
-                topk_budget_np = self.kv_compression_topk_budget_np[:num_reqs]
-                topk_budget_np.fill(0)
-
-                for req_idx in range(num_reqs):
-                    qlen = int(num_scheduled_tokens[req_idx])
-                    if qlen <= 0:
-                        continue
-                    start = 0 if req_idx == 0 else int(
-                        cu_num_tokens[req_idx - 1])
-                    end = int(cu_num_tokens[req_idx])
-                    assert end - start == qlen
-
-                    base_pos = int(self.input_batch.num_computed_tokens_cpu[req_idx])
-                    prompt_len = int(self.input_batch.num_prompt_tokens[req_idx])
-                    end_pos = base_pos + qlen
-                    pos = base_pos + np.arange(qlen, dtype=np.int64)
-
-                    prompt_mask = pos < prompt_len
-                    # Decode tokens are always kept.
-                    must_keep = ~prompt_mask
-
-                    if np.any(prompt_mask):
-                        suffix_start = max(prompt_len - protected_suffix, 0)
-                        must_keep |= prompt_mask & (pos < protected_prefix)
-                        must_keep |= prompt_mask & (pos >= suffix_start)
-                        if keep_last:
-                            last = prompt_len - 1
-                            if base_pos <= last < end_pos:
-                                must_keep[last - base_pos] = True
-
-                        topk_budget_np[req_idx] = compute_topk_budget_step(
-                            prompt_len=prompt_len,
-                            start_pos=base_pos,
-                            end_pos=end_pos,
-                            protected_prefix=protected_prefix,
-                            protected_suffix=protected_suffix,
-                            keep_last_token=keep_last,
-                            prompt_ratio=prompt_ratio,
-                            prompt_budget=prompt_budget,
+            kv_positions_np = maybe_prepare_kv_compression_for_runner_step(
+                runner=self,
+                num_reqs=num_reqs,
+                total_num_scheduled_tokens=total_num_scheduled_tokens,
+                num_scheduled_tokens=num_scheduled_tokens,
+                cu_num_tokens=cu_num_tokens,
+                req_indices=req_indices,
+                arange=arange,
             )
-
-                    must_keep_np[start:end] = must_keep
-
-                # Decode-only fast path: if all scheduled tokens are
-                # unconditionally kept and there is no Top-K budget, KV
-                # compaction is a no-op and we can skip score/topk/dst entirely
-                # in the attention backend.
-                self.kv_compression_needs_compaction = (
-                    (not must_keep_np.all()) or (topk_budget_np > 0).any())
         else:
+            kv_positions_np = None
             self.kv_compression_needs_compaction = False
 
         # Calculate M-RoPE positions.
@@ -910,8 +754,15 @@ class GPUModelRunnerBase(LoRAModelRunnerMixin):
             block_size = kv_cache_group_spec.kv_cache_spec.block_size
             block_table: BlockTable = self.input_batch.block_table[
                 kv_cache_group_id]
-            slot_positions_np = (kv_positions_np
-                                 if use_kv_compression else positions_np)
+            if use_kv_compression:
+                fill_block_table_slot_mapping_np(
+                    block_table=block_table,
+                    req_indices=req_indices,
+                    slot_positions_np=kv_positions_np,
+                    total_num_scheduled_tokens=total_num_scheduled_tokens,
+                    block_size=block_size,
+                )
+            else:
                 # E.g., [0, 1, 0, 1, 2, 3, 4, 0, 1, 2]
                 # -> [0, 0, K, K, K + 1, K + 1, K + 2, 2 * K, 2 * K, 2 * K + 1]
                 # where K is the max_num_blocks_per_req and the block size is 2.
@@ -920,11 +771,11 @@ class GPUModelRunnerBase(LoRAModelRunnerMixin):
                 # block_size.
                 block_table_indices = (
                     req_indices * block_table.max_num_blocks_per_req +
-                slot_positions_np // block_size)
+                    positions_np // block_size)
                 block_table_cpu = block_table.get_cpu_tensor()
                 block_numbers = block_table_cpu.flatten(
                 )[block_table_indices].numpy()
-            block_offsets = slot_positions_np % block_size
+                block_offsets = positions_np % block_size
                 np.add(
                     block_numbers * block_size,
                     block_offsets,
@@ -962,27 +813,10 @@ class GPUModelRunnerBase(LoRAModelRunnerMixin):
         self.seq_lens[:num_reqs].copy_(self.seq_lens_cpu[:num_reqs],
                                        non_blocking=True)
         if use_kv_compression:
-            if self.scheduler_config.chunked_prefill_enabled:
-                self.kv_compression_prompt_end[:num_reqs].copy_(
-                    self.kv_compression_prompt_end_cpu[:num_reqs],
-                    non_blocking=True,
-                )
-                self.kv_compression_prompt_lens[:num_reqs].copy_(
-                    self.kv_compression_prompt_lens_cpu[:num_reqs],
-                    non_blocking=True,
-                )
-                self.kv_compression_prompt_topk_keep[:num_reqs].copy_(
-                    self.kv_compression_prompt_topk_keep_cpu[:num_reqs],
-                    non_blocking=True,
-                )
-            elif self.kv_compression_needs_compaction:
-                self.kv_compression_must_keep[:total_num_scheduled_tokens].copy_(
-                    self.kv_compression_must_keep_cpu[:total_num_scheduled_tokens],
-                    non_blocking=True,
-                )
-                self.kv_compression_topk_budget[:num_reqs].copy_(
-                    self.kv_compression_topk_budget_cpu[:num_reqs],
-                    non_blocking=True,
+            maybe_copy_kv_compression_step_tensors_to_gpu(
+                runner=self,
+                num_reqs=num_reqs,
+                total_num_scheduled_tokens=total_num_scheduled_tokens,
             )
 
         # Fill unused with -1. Needed for reshape_and_cache
@@ -1593,151 +1427,11 @@ class GPUModelRunnerBase(LoRAModelRunnerMixin):
 
     def _stash_kv_compression_prompt_payload(self) -> None:
         """Persist prompt-end compaction indices from the forward context."""
-        if (not envs.VLLM_ENABLE_KV_COMPRESSION
-                or not self.scheduler_config.chunked_prefill_enabled):
-            return
-        forward_context = get_forward_context()
-        payload = getattr(forward_context, "_kv_compression_prompt_payload",
-                          None)
-        if payload is None:
-            return
-
-        req_indices = payload.get("req_indices")
-        idx_sorted = payload.get("idx_sorted")
-        keep_len = payload.get("keep_len")
-        prompt_lens = payload.get("prompt_lens")
-        if (req_indices is None or idx_sorted is None or keep_len is None
-                or prompt_lens is None):
-            return
-
-        req_indices_cpu = req_indices.to(device="cpu",
-                                         dtype=torch.int64).tolist()
-        keep_cpu = keep_len.to(device="cpu", dtype=torch.int64).tolist()
-        prompt_cpu = prompt_lens.to(device="cpu", dtype=torch.int64).tolist()
-        for i, b in enumerate(req_indices_cpu):
-            if b < 0 or b >= len(self.input_batch.req_ids):
-                continue
-            req_id = self.input_batch.req_ids[b]
-            if req_id is None:
-                continue
-            rs = self.requests.get(req_id)
-            if rs is None:
-                continue
-            rs.kv_compression_prompt_idx_sorted = idx_sorted[i]
-            rs.kv_compression_prompt_keep_len = int(keep_cpu[i])
-            rs.kv_compression_prompt_prompt_len = int(prompt_cpu[i])
+        stash_kv_compression_prompt_payload_to_requests(runner=self)
 
     def _maybe_apply_kv_compression_prompt_compaction(self) -> None:
         """Apply one-shot prompt KV compaction before the first decode step."""
-        if (not envs.VLLM_ENABLE_KV_COMPRESSION
-                or not self.scheduler_config.chunked_prefill_enabled):
-            return
-
-        pending_req_ids: list[str] = []
-        for req_id in self.input_batch.req_ids:
-            if req_id is None:
-                continue
-            rs = self.requests.get(req_id)
-            if rs is None:
-                continue
-            if rs.kv_compression_prompt_idx_sorted is None:
-                continue
-            # Only apply once the prompt is fully ingested (decode stage).
-            if rs.num_computed_tokens < rs.num_prompt_tokens:
-                continue
-            pending_req_ids.append(req_id)
-
-        if not pending_req_ids:
-            return
-
-        device = self.device
-        pending_states: list[tuple[str, torch.Tensor, int]] = []
-        for req_id in pending_req_ids:
-            rs = self.requests[req_id]
-            keep = rs.kv_compression_prompt_keep_len
-            idx = rs.kv_compression_prompt_idx_sorted
-            if keep is None or idx is None:
-                continue
-            keep_i = int(keep)
-            if keep_i <= 0:
-                # No prompt tokens kept; clear and skip.
-                rs.kv_compression_prompt_idx_sorted = None
-                rs.kv_compression_prompt_keep_len = None
-                rs.kv_compression_prompt_prompt_len = None
-                continue
-            pending_states.append((req_id, idx, keep_i))
-
-        if not pending_states:
-            return
-
-        B = len(pending_states)
-        keep_list = [k for _, _, k in pending_states]
-        K_max = max(keep_list)
-        idx_batch = torch.zeros((B, K_max), device=device, dtype=torch.int32)
-        for i, (_, row, k) in enumerate(pending_states):
-            idx_batch[i, :k] = row[:k].to(device=device, dtype=torch.int32)
-        keep_tensor = torch.tensor(keep_list, device=device, dtype=torch.int32)
-
-        from vllm.v1.attention.kv_compression.kv_cache_triton import (
-            front_compact_inplace_fa_triton, make_fa_cache_view)
-
-        # Apply compaction to every attention layer's KV cache in-place.
-        for group_id, kv_cache_group_spec in enumerate(
-                self.kv_cache_config.kv_cache_groups):
-            max_blocks = 0
-            for req_id, _, _ in pending_states:
-                rs = self.requests[req_id]
-                if group_id >= len(rs.block_ids):
-                    continue
-                max_blocks = max(max_blocks, len(rs.block_ids[group_id]))
-            if max_blocks == 0:
-                continue
-
-            block_table_cpu = torch.zeros((B, max_blocks),
-                                          dtype=torch.int32,
-                                          device="cpu")
-            for i, (req_id, _, _) in enumerate(pending_states):
-                rs = self.requests[req_id]
-                if group_id >= len(rs.block_ids):
-                    continue
-                ids = rs.block_ids[group_id]
-                if ids:
-                    block_table_cpu[i, :len(ids)] = torch.tensor(
-                        ids, dtype=torch.int32, device="cpu")
-            block_table = block_table_cpu.to(device=device, non_blocking=True)
-
-            for layer_name in kv_cache_group_spec.layer_names:
-                layer_index = self._extract_layer_index(layer_name)
-                if layer_index >= len(self.kv_caches):
-                    continue
-                kv_cache = self.kv_caches[layer_index]
-                if not current_platform.is_rocm():
-                    if not isinstance(kv_cache, torch.Tensor):
-                        continue
-                    key_cache, value_cache = kv_cache.unbind(0)
-                else:
-                    if (not isinstance(kv_cache, (tuple, list))
-                            or len(kv_cache) != 2):
-                        continue
-                    key_cache, value_cache = kv_cache
-                k_view, v_view = make_fa_cache_view(key_cache=key_cache,
-                                                    value_cache=value_cache)
-                front_compact_inplace_fa_triton(
-                    k_view,
-                    v_view,
-                    block_table,
-                    idx_batch,
-                    keep_tensor,
-                )
-
-        # Clear pending state after successful compaction.
-        for req_id, _, _ in pending_states:
-            rs = self.requests.get(req_id)
-            if rs is None:
-                continue
-            rs.kv_compression_prompt_idx_sorted = None
-            rs.kv_compression_prompt_keep_len = None
-            rs.kv_compression_prompt_prompt_len = None
+        maybe_apply_kv_compression_prompt_compaction(runner=self)
 
     @torch.inference_mode()
     def execute_model(
@@ -1839,19 +1533,7 @@ class GPUModelRunnerBase(LoRAModelRunnerMixin):
         # the first decode step writes/reads KV at the compressed positions.
         self._maybe_apply_kv_compression_prompt_compaction()
 
-        use_tbo = (envs.VLLM_ENABLE_TBO and scheduler_output.total_num_scheduled_tokens
-                   >= envs.VLLM_TBO_MIN_TOKENS)
-        if (use_tbo and envs.VLLM_ENABLE_KV_COMPRESSION
-                and self.scheduler_config.chunked_prefill_enabled):
-            # NOTE: the TBO path does not call `_stash_kv_compression_prompt_payload`
-            # inside its `set_forward_context`, so scheme-3 prompt-end payloads
-            # would be dropped and the next-step compaction would never run.
-            logger.warning_once(
-                "TBO is currently incompatible with chunked prefill KV "
-                "compression (scheme 3); running without TBO.")
-            use_tbo = False
-
-        if use_tbo:
+        if envs.VLLM_ENABLE_TBO and scheduler_output.total_num_scheduled_tokens >= envs.VLLM_TBO_MIN_TOKENS: 
             model_output, finished_sending, finished_recving = \
                  tbo_split_and_execute_model(self, attn_metadata, num_input_tokens,
                                              num_tokens_across_dp, input_ids, positions,
@@ -3476,119 +3158,22 @@ class GPUModelRunnerMTP(GPUModelRunnerBase):
         np.add(self.input_batch.num_computed_tokens_cpu[req_indices],
                arange,
                out=positions_np)
-
         # KV positions (where the KV for each scheduled token is temporarily
         # written). When KV compression is enabled, KV positions are decoupled
         # from logical positions.
         use_kv_compression = envs.VLLM_ENABLE_KV_COMPRESSION
         if use_kv_compression:
-            kv_positions_np = self.kv_positions_np[:total_num_scheduled_tokens]
-            np.add(self.input_batch.num_kv_tokens_cpu[req_indices],
-                   arange,
-                   out=kv_positions_np)
-        else:
-            kv_positions_np = None
-
-        if use_kv_compression:
-            prompt_ratio = envs.VLLM_KV_COMPRESSION_PROMPT_RATIO
-            prompt_budget = envs.VLLM_KV_COMPRESSION_PROMPT_BUDGET
-            protected_prefix = envs.VLLM_KV_COMPRESSION_PROTECTED_PREFIX
-            protected_suffix = envs.VLLM_KV_COMPRESSION_PROTECTED_SUFFIX
-            keep_last = envs.VLLM_KV_COMPRESSION_KEEP_LAST_TOKEN
-
-            if self.scheduler_config.chunked_prefill_enabled:
-                # Scheme 3: with chunked prefill, defer compaction until after
-                # the full prompt is ingested. Otherwise, the next prefill chunk
-                # would attend to a truncated history and quality can collapse.
-                prompt_end_np = self.kv_compression_prompt_end_np[:num_reqs]
-                prompt_end_np.fill(False)
-                prompt_lens_np = self.kv_compression_prompt_lens_np[:num_reqs]
-                prompt_lens_np.fill(0)
-                topk_keep_np = self.kv_compression_prompt_topk_keep_np[:num_reqs]
-                topk_keep_np.fill(0)
-
-                for req_idx in range(num_reqs):
-                    qlen = int(num_scheduled_tokens[req_idx])
-                    if qlen <= 0:
-                        continue
-                    base_pos = int(
-                        self.input_batch.num_computed_tokens_cpu[req_idx])
-                    prompt_len = int(self.input_batch.num_prompt_tokens[req_idx])
-                    end_pos = base_pos + qlen
-                    ends_prompt = (base_pos < prompt_len) and (end_pos >=
-                                                              prompt_len)
-                    if not ends_prompt:
-                        continue
-
-                    prompt_end_np[req_idx] = True
-                    prompt_lens_np[req_idx] = prompt_len
-                    topk_keep_np[req_idx] = compute_prompt_topk_keep_total(
-                        prompt_len=prompt_len,
-                        protected_prefix=protected_prefix,
-                        protected_suffix=protected_suffix,
-                        keep_last_token=keep_last,
-                        prompt_ratio=prompt_ratio,
-                        prompt_budget=prompt_budget,
-                    )
-
-                self.kv_compression_prompt_topk_keep_max = int(
-                    topk_keep_np[:num_reqs].max()) if num_reqs > 0 else 0
-                self.kv_compression_needs_compaction = False
-            else:
-                must_keep_np = self.kv_compression_must_keep_np[
-                    :total_num_scheduled_tokens]
-                must_keep_np.fill(False)
-                topk_budget_np = self.kv_compression_topk_budget_np[:num_reqs]
-                topk_budget_np.fill(0)
-
-                for req_idx in range(num_reqs):
-                    qlen = int(num_scheduled_tokens[req_idx])
-                    if qlen <= 0:
-                        continue
-                    start = 0 if req_idx == 0 else int(
-                        cu_num_tokens[req_idx - 1])
-                    end = int(cu_num_tokens[req_idx])
-                    assert end - start == qlen
-
-                    base_pos = int(
-                        self.input_batch.num_computed_tokens_cpu[req_idx])
-                    prompt_len = int(self.input_batch.num_prompt_tokens[req_idx])
-                    end_pos = base_pos + qlen
-                    pos = base_pos + np.arange(qlen, dtype=np.int64)
-
-                    prompt_mask = pos < prompt_len
-                    # Decode tokens are always kept.
-                    must_keep = ~prompt_mask
-
-                    if np.any(prompt_mask):
-                        suffix_start = max(prompt_len - protected_suffix, 0)
-                        must_keep |= prompt_mask & (pos < protected_prefix)
-                        must_keep |= prompt_mask & (pos >= suffix_start)
-                        if keep_last:
-                            last = prompt_len - 1
-                            if base_pos <= last < end_pos:
-                                must_keep[last - base_pos] = True
-
-                        topk_budget_np[req_idx] = compute_topk_budget_step(
-                            prompt_len=prompt_len,
-                            start_pos=base_pos,
-                            end_pos=end_pos,
-                            protected_prefix=protected_prefix,
-                            protected_suffix=protected_suffix,
-                            keep_last_token=keep_last,
-                            prompt_ratio=prompt_ratio,
-                            prompt_budget=prompt_budget,
+            kv_positions_np = maybe_prepare_kv_compression_for_runner_step(
+                runner=self,
+                num_reqs=num_reqs,
+                total_num_scheduled_tokens=total_num_scheduled_tokens,
+                num_scheduled_tokens=num_scheduled_tokens,
+                cu_num_tokens=cu_num_tokens,
+                req_indices=req_indices,
+                arange=arange,
             )
-
-                    must_keep_np[start:end] = must_keep
-
-                # Decode-only fast path: if all scheduled tokens are
-                # unconditionally kept and there is no Top-K budget, KV
-                # compaction is a no-op and we can skip score/topk/dst entirely
-                # in the attention backend.
-                self.kv_compression_needs_compaction = (
-                    (not must_keep_np.all()) or (topk_budget_np > 0).any())
         else:
+            kv_positions_np = None
             self.kv_compression_needs_compaction = False
 
         # Calculate M-RoPE positions.
@@ -3610,15 +3195,21 @@ class GPUModelRunnerMTP(GPUModelRunnerBase):
                            0,
                            torch.from_numpy(token_indices),
                            out=self.input_ids_cpu[:total_num_scheduled_tokens])
-
         # Calculate the slot mapping for each KV cache group.
         for kv_cache_group_id, kv_cache_group_spec in enumerate(
                 self.kv_cache_config.kv_cache_groups):
             block_size = kv_cache_group_spec.kv_cache_spec.block_size
             block_table: BlockTable = self.input_batch.block_table[
                 kv_cache_group_id]
-            slot_positions_np = (kv_positions_np
-                                 if use_kv_compression else positions_np)
+            if use_kv_compression:
+                fill_block_table_slot_mapping_np(
+                    block_table=block_table,
+                    req_indices=req_indices,
+                    slot_positions_np=kv_positions_np,
+                    total_num_scheduled_tokens=total_num_scheduled_tokens,
+                    block_size=block_size,
+                )
+            else:
                 # E.g., [0, 1, 0, 1, 2, 3, 4, 0, 1, 2]
                 # -> [0, 0, K, K, K + 1, K + 1, K + 2, 2 * K, 2 * K, 2 * K + 1]
                 # where K is the max_num_blocks_per_req and the block size is 2.
@@ -3627,11 +3218,11 @@ class GPUModelRunnerMTP(GPUModelRunnerBase):
                 # block_size.
                 block_table_indices = (
                     req_indices * block_table.max_num_blocks_per_req +
-                    slot_positions_np // block_size)
+                    positions_np // block_size)
                 block_table_cpu = block_table.get_cpu_tensor()
                 block_numbers = block_table_cpu.flatten(
                 )[block_table_indices].numpy()
-            block_offsets = slot_positions_np % block_size
+                block_offsets = positions_np % block_size
                 np.add(
                     block_numbers * block_size,
                     block_offsets,
@@ -3669,27 +3260,10 @@ class GPUModelRunnerMTP(GPUModelRunnerBase):
         self.seq_lens[:num_reqs].copy_(self.seq_lens_cpu[:num_reqs],
                                        non_blocking=True)
         if use_kv_compression:
-            if self.scheduler_config.chunked_prefill_enabled:
-                self.kv_compression_prompt_end[:num_reqs].copy_(
-                    self.kv_compression_prompt_end_cpu[:num_reqs],
-                    non_blocking=True,
-                )
-                self.kv_compression_prompt_lens[:num_reqs].copy_(
-                    self.kv_compression_prompt_lens_cpu[:num_reqs],
-                    non_blocking=True,
-                )
-                self.kv_compression_prompt_topk_keep[:num_reqs].copy_(
-                    self.kv_compression_prompt_topk_keep_cpu[:num_reqs],
-                    non_blocking=True,
-                )
-            elif self.kv_compression_needs_compaction:
-                self.kv_compression_must_keep[:total_num_scheduled_tokens].copy_(
-                    self.kv_compression_must_keep_cpu[:total_num_scheduled_tokens],
-                    non_blocking=True,
-                )
-                self.kv_compression_topk_budget[:num_reqs].copy_(
-                    self.kv_compression_topk_budget_cpu[:num_reqs],
-                    non_blocking=True,
+            maybe_copy_kv_compression_step_tensors_to_gpu(
+                runner=self,
+                num_reqs=num_reqs,
+                total_num_scheduled_tokens=total_num_scheduled_tokens,
             )
 
         # Fill unused with -1. Needed for reshape_and_cache
@@ -3877,16 +3451,7 @@ class GPUModelRunnerMTP(GPUModelRunnerBase):
         # the first decode step writes/reads KV at the compressed positions.
         self._maybe_apply_kv_compression_prompt_compaction()
 
-        use_tbo = (envs.VLLM_ENABLE_TBO and scheduler_output.total_num_scheduled_tokens
-                   >= envs.VLLM_TBO_MIN_TOKENS)
-        if (use_tbo and envs.VLLM_ENABLE_KV_COMPRESSION
-                and self.scheduler_config.chunked_prefill_enabled):
-            logger.warning_once(
-                "TBO is currently incompatible with chunked prefill KV "
-                "compression (scheme 3); running without TBO.")
-            use_tbo = False
-
-        if use_tbo:
+        if envs.VLLM_ENABLE_TBO and scheduler_output.total_num_scheduled_tokens >= envs.VLLM_TBO_MIN_TOKENS:
             model_output, finished_sending, finished_recving = \
                 tbo_split_and_execute_model(self, attn_metadata, num_input_tokens,
                                             num_tokens_across_dp, input_ids, positions,

vllm/v1/worker/slot_mapping_utils.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from __future__ import annotations
+
+import numpy as np
+
+from vllm.v1.worker.block_table import BlockTable
+
+
+def fill_block_table_slot_mapping_np(
+    *,
+    block_table: BlockTable,
+    req_indices: np.ndarray,  # [T] int64
+    slot_positions_np: np.ndarray,  # [T] int64
+    total_num_scheduled_tokens: int,
+    block_size: int,
+) -> None:
+    """Fill `block_table.slot_mapping_np` for a packed batch of tokens."""
+    block_table_indices = (req_indices * block_table.max_num_blocks_per_req +
+                           slot_positions_np // int(block_size))
+    block_table_cpu = block_table.get_cpu_tensor()
+    block_numbers = block_table_cpu.flatten()[block_table_indices].numpy()
+    block_offsets = slot_positions_np % int(block_size)
+    np.add(
+        block_numbers * int(block_size),
+        block_offsets,
+        out=block_table.slot_mapping_np[:total_num_scheduled_tokens],
+    )
+