# Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
# SPDX-License-Identifier: BSD-3-Clause

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"""
MoE Persistent Tile Scheduler

A specialized tile scheduler for MoE (Mixture of Experts) grouped GEMM operations.
This scheduler handles tile iteration across all experts, producing MoEWorkTileInfo
(expert_idx, tile_m_idx, tile_n_idx, k_tile_cnt) for each tile.

Scenarios:
- 2Dx3D (Forward): A(tokens_sum, hidden) x B(experts, intermediate, hidden) -> C(tokens_sum, intermediate)
- 2Dx2D (Backward): A(intermediate, tokens_sum) x B(hidden, tokens_sum) -> C(experts, intermediate, hidden)

Key design principle:
- Scheduler is ONLY responsible for tile iteration (tensor-agnostic, TMA-agnostic)
- Domain conversion (fake tensor -> real expert tensor) is handled by MoESchedExtension
- TMA descriptor management is handled by OnlineTensormapDescCreator
- The kernel orchestrates all three components
"""

from typing import List, Tuple, Literal

import cutlass
import cutlass.cute as cute
from cutlass.cutlass_dsl import (
    Boolean,
    Int32,
    Integer,
    extract_mlir_values,
    new_from_mlir_values,
    const_expr,
    dsl_user_op,
)
from cutlass._mlir import ir

# =============================================================================
# Work Tile Info
# =============================================================================

class MoEWorkTileInfo:
    """
    Work tile information for MoE scheduler.
    
    Contains CTA-level tile information for executor warps:
    - expert_idx: Which expert (-1 means invalid/done)
    - tile_m_idx: CTA tile index along GEMM M dimension
    - tile_n_idx: CTA tile index along GEMM N dimension  
    - k_tile_cnt: Number of CTA tiles along K dimension
    
    Note: These are CTA-level indices, not cluster-level.
    tile_l_idx is always 0 for MoE, executor can hardcode it.
    
    For 2Dx3D (Forward):
        M = tokens_i (dynamic), N = intermediate (fixed), K = hidden (fixed)
    
    For 2Dx2D (Backward):
        M = intermediate (fixed), N = hidden (fixed), K = tokens_i (dynamic)
    """
    
    def __init__(
        self,
        expert_idx: Int32,      # -1 means invalid tile
        tile_m_idx: Int32,
        tile_n_idx: Int32,
        k_tile_cnt: Int32,
    ):
        self.expert_idx = expert_idx
        self.tile_m_idx = tile_m_idx
        self.tile_n_idx = tile_n_idx
        self.k_tile_cnt = k_tile_cnt
    
    @property
    def is_valid_tile(self) -> Boolean:
        """Check if this is a valid work tile (expert_idx >= 0)."""
        return self.expert_idx >= Int32(0)
    
    def __extract_mlir_values__(self) -> List[ir.Value]:
        values = extract_mlir_values(self.expert_idx)
        values.extend(extract_mlir_values(self.tile_m_idx))
        values.extend(extract_mlir_values(self.tile_n_idx))
        values.extend(extract_mlir_values(self.k_tile_cnt))
        return values
    
    def __new_from_mlir_values__(self, values: List[ir.Value]) -> "MoEWorkTileInfo":
        assert len(values) == 4
        return MoEWorkTileInfo(
            expert_idx=new_from_mlir_values(self.expert_idx, [values[0]]),
            tile_m_idx=new_from_mlir_values(self.tile_m_idx, [values[1]]),
            tile_n_idx=new_from_mlir_values(self.tile_n_idx, [values[2]]),
            k_tile_cnt=new_from_mlir_values(self.k_tile_cnt, [values[3]]),
        )
    
    def to_rmem_tensor(self):
        """Pack work tile info fields into an rmem tensor of shape (4,) for vectorized smem copy."""
        rmem = cute.make_rmem_tensor((4,), Int32)
        rmem[0] = self.expert_idx
        rmem[1] = self.tile_m_idx
        rmem[2] = self.tile_n_idx
        rmem[3] = self.k_tile_cnt
        return rmem
    
    @staticmethod
    def from_rmem_tensor(rmem) -> "MoEWorkTileInfo":
        """Unpack work tile info from an rmem tensor of shape (4,)."""
        return MoEWorkTileInfo(
            expert_idx=rmem[0],  # type: ignore[arg-type]
            tile_m_idx=rmem[1],  # type: ignore[arg-type]
            tile_n_idx=rmem[2],  # type: ignore[arg-type]
            k_tile_cnt=rmem[3],  # type: ignore[arg-type]
        )


# =============================================================================
# Scheduler Parameters
# =============================================================================

class MoEStaticSchedulerParams:
    """
    Parameters for MoE tile scheduler.
    
    Uses unified semantics for both scenarios:
    - expert_shape: (expert_cnt, intermediate, hidden)
    
    For 2Dx3D: GEMM is (M=tokens_i, N=intermediate, K=hidden) per expert
    For 2Dx2D: GEMM is (M=hidden, N=intermediate, K=tokens_i) per expert
    
    Tile hierarchy:
    - cta_tile_shape_mnk: Single CTA tile shape (tile_m, tile_n, tile_k)
    - cluster_shape_mn: CTAs per cluster (cluster_m, cluster_n)
    - cluster_tile_shape_mn: Cluster tile shape = cta_tile_shape * cluster_shape
    
    This class is used both on host (for grid shape calculation) and on device
    (stored in scheduler). Codegen-time constants (scenario, cta_tile_shape_mnk,
    cluster_shape_mn) are NOT serialized to MLIR values.
    """
    
    def __init__(
        self,
        scenario: Literal["2Dx3D", "2Dx2D"],
        expert_shape: Tuple[int | Int32, int | Int32, int | Int32],  # (expert_cnt, intermediate, hidden)
        cta_tile_shape_mnk: Tuple[int, int, int],  # (tile_m, tile_n, tile_k)
        cluster_shape_mn: Tuple[int, int],         # (cluster_m, cluster_n)
    ):
        self.scenario = scenario
        e, i, h = expert_shape
        self.expert_cnt = e if isinstance(e, Int32) else Int32(e)
        self.intermediate = i if isinstance(i, Int32) else Int32(i)
        self.hidden = h if isinstance(h, Int32) else Int32(h)
        self.cta_tile_shape_mnk = cta_tile_shape_mnk
        self.cluster_shape_mn = cluster_shape_mn
    
    @property
    def cluster_tile_m(self) -> int:
        """Cluster tile size along M = cta_tile_m * cluster_m."""
        return self.cta_tile_shape_mnk[0] * self.cluster_shape_mn[0]
    
    @property
    def cluster_tile_n(self) -> int:
        """Cluster tile size along N = cta_tile_n * cluster_n."""
        return self.cta_tile_shape_mnk[1] * self.cluster_shape_mn[1]
    
    @property
    def cta_tile_k(self) -> int:
        """CTA tile size along K (same as cluster since cluster_k = 1)."""
        return self.cta_tile_shape_mnk[2]
    
    def __extract_mlir_values__(self) -> List[ir.Value]:
        """Only serialize runtime values, not codegen-time constants."""
        values = []
        values.extend(extract_mlir_values(self.expert_cnt))
        values.extend(extract_mlir_values(self.intermediate))
        values.extend(extract_mlir_values(self.hidden))
        return values
    
    def __new_from_mlir_values__(self, values: List[ir.Value]) -> "MoEStaticSchedulerParams":
        assert len(values) == 3
        return MoEStaticSchedulerParams(
            scenario=self.scenario,
            expert_shape=(
                new_from_mlir_values(self.expert_cnt, [values[0]]),
                new_from_mlir_values(self.intermediate, [values[1]]),
                new_from_mlir_values(self.hidden, [values[2]]),
            ),
            cta_tile_shape_mnk=self.cta_tile_shape_mnk,
            cluster_shape_mn=self.cluster_shape_mn,
        )
    
    @staticmethod
    def get_grid_shape(
        params: "MoEStaticSchedulerParams",
        max_active_clusters: int,
    ) -> Tuple[int, int, int]:
        """
        Compute grid shape for kernel launch.
        
        Since host doesn't know token distribution across experts,
        we launch max_active_clusters and let device-side scheduler
        determine which tiles are valid.
        """
        return (
            params.cluster_shape_mn[0],
            params.cluster_shape_mn[1],
            max_active_clusters,
        )


# =============================================================================
# Scheduler (Device-side)
# =============================================================================

class MoEStaticPersistentTileScheduler:
    """
    Persistent tile scheduler specialized for MoE grouped GEMM.

    This scheduler is ONLY responsible for tile iteration. It does NOT know
    about tensor types, TMA descriptors, or domain conversion. Those concerns
    are handled by MoESchedExtension and OnlineTensormapDescCreator respectively.

    Architecture:
    - Scheduler warp: Holds scheduler instance, iterates tiles, broadcasts work_tile_info
    - Executor warps: Read work_tile_info from smem, use MoESchedExtension for
      domain conversion and TMA desc selection

    The scheduler handles:
    - 2Dx3D: Dynamic M per expert (from offs), fixed N (intermediate) and K (hidden)
    - 2Dx2D: Fixed M (intermediate) and N (hidden), dynamic K per expert (reduction axis)

    Usage (Scheduler warp):
        scheduler = MoEStaticPersistentTileScheduler.create(params, offs, block_idx, grid_dim)
        work_tile_info = scheduler.initial_work_tile_info()
        # Broadcast work_tile_info to smem...

        while work_tile_info.is_valid_tile:
            # ... do work ...
            work_tile_info = scheduler.advance_to_next_work()
            # Broadcast work_tile_info to smem...

    Usage (Executor warps - via MoESchedExtension):
        # Read work_tile_info from smem...
        real_a, desc_a = ext.get_gmem_tensor("a", tma_tensor_a, offs, work_tile_info)
        real_b, desc_b = ext.get_gmem_tensor("b", tma_tensor_b, offs, work_tile_info)
        real_c, desc_c = ext.get_gmem_tensor("c", tma_tensor_c, offs, work_tile_info)
    """
    
    def __init__(
        self,
        # Params (contains scenario, expert_cnt, intermediate, hidden, tile/cluster shapes)
        params: MoEStaticSchedulerParams,
        # Runtime tensor for scheduling
        offs: cute.Tensor,             # (experts,) cumsum of token counts
        # Scheduling state
        num_persistent_clusters: Int32,
        current_work_linear_idx: Int32,
        cta_id_in_cluster: cute.Coord,
        # Expert tracking state (for O(1) advance within same expert)
        current_expert_idx: Int32,
        expert_tile_start: Int32,      # cumsum of tiles before current expert
        expert_tile_end: Int32,        # cumsum of tiles including current expert
    ):
        self.params = params
        self.offs = offs
        self.num_persistent_clusters = num_persistent_clusters
        self._current_work_linear_idx = current_work_linear_idx
        self.cta_id_in_cluster = cta_id_in_cluster
        # Expert tracking
        self.current_expert_idx = current_expert_idx
        self.expert_tile_start = expert_tile_start
        self.expert_tile_end = expert_tile_end
    
    # =========================================================================
    # Convenience accessors for params
    # =========================================================================
    
    @property
    def scenario(self) -> Literal["2Dx3D", "2Dx2D"]:
        return self.params.scenario
    
    @property
    def expert_cnt(self) -> Int32:
        return self.params.expert_cnt
    
    @property
    def intermediate(self) -> Int32:
        return self.params.intermediate
    
    @property
    def hidden(self) -> Int32:
        return self.params.hidden
    
    @property
    def cta_tile_shape_mnk(self) -> Tuple[int, int, int]:
        return self.params.cta_tile_shape_mnk
    
    @property
    def cluster_shape_mn(self) -> Tuple[int, int]:
        return self.params.cluster_shape_mn
    
    @property
    def cluster_tile_m(self) -> int:
        return self.params.cluster_tile_m
    
    @property
    def cluster_tile_n(self) -> int:
        return self.params.cluster_tile_n
    
    @property
    def cta_tile_k(self) -> int:
        return self.params.cta_tile_k
    
    # =========================================================================
    # MLIR value serialization (for SSA value passing in device code)
    # =========================================================================
    
    def __extract_mlir_values__(self) -> List[ir.Value]:
        values = []
        # Params (only runtime values are extracted)
        values.extend(extract_mlir_values(self.params))
        # Runtime tensor for scheduling
        values.extend(extract_mlir_values(self.offs))
        # Scheduling state
        values.extend(extract_mlir_values(self.num_persistent_clusters))
        values.extend(extract_mlir_values(self._current_work_linear_idx))
        values.extend(extract_mlir_values(self.cta_id_in_cluster))
        # Expert tracking state
        values.extend(extract_mlir_values(self.current_expert_idx))
        values.extend(extract_mlir_values(self.expert_tile_start))
        values.extend(extract_mlir_values(self.expert_tile_end))
        return values
    
    def __new_from_mlir_values__(
        self, values: List[ir.Value]
    ) -> "MoEStaticPersistentTileScheduler":
        idx = 0
        
        # Params (3 values: expert_cnt, intermediate, hidden)
        new_params = new_from_mlir_values(self.params, values[idx:idx + 3])
        idx += 3
        
        # Runtime tensor for scheduling (variable size)
        offs_len = len(extract_mlir_values(self.offs))
        new_offs = new_from_mlir_values(self.offs, values[idx:idx + offs_len])
        idx += offs_len
        
        # Scheduling state
        new_num_persistent_clusters = new_from_mlir_values(
            self.num_persistent_clusters, [values[idx]]
        )
        idx += 1
        new_current_work_linear_idx = new_from_mlir_values(
            self._current_work_linear_idx, [values[idx]]
        )
        idx += 1
        
        # cta_id_in_cluster (3 values for Coord)
        new_cta_id_in_cluster = new_from_mlir_values(
            self.cta_id_in_cluster, values[idx:idx + 3]
        )
        idx += 3
        
        # Expert tracking state
        new_current_expert_idx = new_from_mlir_values(
            self.current_expert_idx, [values[idx]]
        )
        idx += 1
        new_expert_tile_start = new_from_mlir_values(
            self.expert_tile_start, [values[idx]]
        )
        idx += 1
        new_expert_tile_end = new_from_mlir_values(
            self.expert_tile_end, [values[idx]]
        )
        idx += 1
        
        return MoEStaticPersistentTileScheduler(
            params=new_params,
            offs=new_offs,
            num_persistent_clusters=new_num_persistent_clusters,
            current_work_linear_idx=new_current_work_linear_idx,
            cta_id_in_cluster=new_cta_id_in_cluster,
            current_expert_idx=new_current_expert_idx,
            expert_tile_start=new_expert_tile_start,
            expert_tile_end=new_expert_tile_end,
        )
    
    # =========================================================================
    # Factory method
    # =========================================================================
    
    @staticmethod
    @dsl_user_op
    def create(
        params: MoEStaticSchedulerParams,
        offs: cute.Tensor,
        block_idx: Tuple[Integer, Integer, Integer],
        grid_dim: Tuple[Integer, Integer, Integer],
        *,
        loc=None,
        ip=None,
    ) -> "MoEStaticPersistentTileScheduler":
        """
        Create a MoE persistent tile scheduler.
        
        :param params: Scheduler parameters (from host)
        :param offs: Cumsum tensor of token counts per expert, shape (experts,)
        :param block_idx: CUDA block index
        :param grid_dim: CUDA grid dimensions
        """
        num_persistent_clusters = cute.size(grid_dim, loc=loc, ip=ip) // cute.size(
            params.cluster_shape_mn, loc=loc, ip=ip
        )
        
        bidx, bidy, bidz = block_idx
        current_work_linear_idx = Int32(bidz)
        
        cta_id_in_cluster = (
            Int32(bidx % params.cluster_shape_mn[0]),
            Int32(bidy % params.cluster_shape_mn[1]),
            Int32(0),
        )
        
        # Initialize expert tracking to "before expert 0"
        # The first call to _get_work_tile_for_linear_idx will advance to the correct expert
        current_expert_idx = Int32(0)
        expert_tile_start = Int32(0)
        expert_tile_end = Int32(0)  # Will be computed on first access
        
        return MoEStaticPersistentTileScheduler(
            params=params,
            offs=offs,
            num_persistent_clusters=num_persistent_clusters,
            current_work_linear_idx=current_work_linear_idx,
            cta_id_in_cluster=cta_id_in_cluster,
            current_expert_idx=current_expert_idx,
            expert_tile_start=expert_tile_start,
            expert_tile_end=expert_tile_end,
        )
    
    # =========================================================================
    # Tile iteration methods
    # =========================================================================
    
    @dsl_user_op
    @cute.jit
    def initial_work_tile_info(self, *, loc=None, ip=None) -> MoEWorkTileInfo:
        """Get the initial work tile info."""
        return self._get_work_tile_for_linear_idx(
            self._current_work_linear_idx, loc=loc, ip=ip
        )
    
    @dsl_user_op
    @cute.jit
    def advance_to_next_work(self, *, loc=None, ip=None) -> MoEWorkTileInfo:
        """Advance to the next work tile and return its info."""
        self._current_work_linear_idx += self.num_persistent_clusters
        return self._get_work_tile_for_linear_idx(
            self._current_work_linear_idx, loc=loc, ip=ip
        )
    
    @dsl_user_op
    @cute.jit
    def _get_work_tile_for_linear_idx(
        self, 
        cluster_linear_idx: Int32, 
        *, 
        loc=None, 
        ip=None
    ) -> MoEWorkTileInfo:
        """
        Convert a linear cluster index to MoEWorkTileInfo.
        
        Uses cached expert tracking state for O(1) fast path when staying
        within the same expert. Advances expert state when needed.
        
        Returns an invalid tile (expert_idx = -1) if cluster_linear_idx is out of range.
        """
        # Ensure expert tracking is initialized and up-to-date
        self._advance_expert_to_contain(cluster_linear_idx, loc=loc, ip=ip)
        
        # Check if valid (still within expert range after advancing)
        is_valid = self.current_expert_idx < self.expert_cnt

        work_tile_info = MoEWorkTileInfo(
            expert_idx=Int32(-1),
            tile_m_idx=Int32(0),
            tile_n_idx=Int32(0),
            k_tile_cnt=Int32(0),
        )
        
        if is_valid:
            # Compute local cluster tile indices within current expert
            local_idx = cluster_linear_idx - self.expert_tile_start
            cluster_tile_m_idx, cluster_tile_n_idx = self._decompose_local_idx(
                local_idx, self.current_expert_idx, loc=loc, ip=ip
            )
            
            # Convert cluster tile indices to CTA tile indices
            # cta_tile_idx = cluster_tile_idx * cluster_shape + cta_id_in_cluster
            cta_tile_m_idx = (
                cluster_tile_m_idx * self.cluster_shape_mn[0]
                + self.cta_id_in_cluster[0]  # type: ignore[index]
            )
            cta_tile_n_idx = (
                cluster_tile_n_idx * self.cluster_shape_mn[1]
                + self.cta_id_in_cluster[1]  # type: ignore[index]
            )
            # Compute k_tile_cnt
            k_tile_cnt = self._compute_k_tile_cnt(self.current_expert_idx, loc=loc, ip=ip)
        
            work_tile_info = MoEWorkTileInfo(
                expert_idx=self.current_expert_idx,
                tile_m_idx=cta_tile_m_idx,
                tile_n_idx=cta_tile_n_idx,
                k_tile_cnt=k_tile_cnt,
            )
        return work_tile_info
    
    @dsl_user_op
    @cute.jit
    def _advance_expert_to_contain(
        self,
        cluster_linear_idx: Int32,
        *,
        loc=None,
        ip=None,
    ) -> None:
        """
        Advance expert tracking state until current expert contains cluster_linear_idx,
        or we run out of experts.
        
        Fast path: If already in correct expert, no work needed.
        """
        # Initialize expert_tile_end if this is the first call (expert_tile_end == 0)
        if self.expert_tile_end == Int32(0):
            tiles_for_expert_0 = self._compute_tiles_for_expert(Int32(0), loc=loc, ip=ip)
            self.expert_tile_end = tiles_for_expert_0
        
        # Advance until cluster_linear_idx < expert_tile_end or no more experts
        while cluster_linear_idx >= self.expert_tile_end and self.current_expert_idx < self.expert_cnt:
            self.current_expert_idx = self.current_expert_idx + 1
            self.expert_tile_start = self.expert_tile_end
            
            if self.current_expert_idx < self.expert_cnt:
                tiles_for_expert = self._compute_tiles_for_expert(
                    self.current_expert_idx, loc=loc, ip=ip
                )
                self.expert_tile_end = self.expert_tile_end + tiles_for_expert
    
    @dsl_user_op
    @cute.jit
    def _compute_tiles_for_expert(
        self,
        expert_idx: Int32,
        *,
        loc=None,
        ip=None,
    ) -> Int32:
        """Compute total cluster tiles for a given expert."""
        if const_expr(self.scenario == "2Dx2D"):
            # Fixed M=hidden, N=intermediate
            cluster_tile_m_cnt = (self.hidden + self.cluster_tile_m - 1) // self.cluster_tile_m
            cluster_tile_n_cnt = (self.intermediate + self.cluster_tile_n - 1) // self.cluster_tile_n
            return cluster_tile_m_cnt * cluster_tile_n_cnt
        else:  # 2Dx3D
            # Variable M (tokens), fixed N
            tokens_i = self.offs[expert_idx]
            if expert_idx > 0:
                tokens_i = tokens_i - self.offs[expert_idx - 1]  # type: ignore[operator]
            cluster_tile_m_cnt = (
                tokens_i + self.cluster_tile_m - 1  # type: ignore[operator]
            ) // self.cluster_tile_m
            cluster_tile_n_cnt = (
                self.intermediate + self.cluster_tile_n - 1
            ) // self.cluster_tile_n
            return cluster_tile_m_cnt * cluster_tile_n_cnt
    
    @dsl_user_op
    @cute.jit
    def _decompose_local_idx(
        self,
        local_idx: Int32,
        expert_idx: Int32,
        *,
        loc=None,
        ip=None,
    ) -> Tuple[Int32, Int32]:
        """
        Decompose local cluster tile index within expert to (cluster_tile_m_idx, cluster_tile_n_idx).
        
        Uses "short side first" strategy: the shorter dimension changes faster.
        This maximizes overlap between adjacent clusters for better L2 cache utilization.
        
        For example, if m_cnt=2, n_cnt=8:
        - N is longer, so M changes faster: local_idx = n_idx * m_cnt + m_idx
        - Linearization order: (0,0), (1,0), (0,1), (1,1), (0,2), (1,2), ...
        """
        # Get tile counts for M and N
        cluster_tile_m_cnt, cluster_tile_n_cnt = self._get_cluster_tile_counts(
            expert_idx, loc=loc, ip=ip
        )
        cluster_tile_m_idx = -1
        cluster_tile_n_idx = -1
        
        # Short side first: shorter dimension changes faster
        # If m_cnt <= n_cnt: m is shorter, m changes faster
        #   local_idx = n_idx * m_cnt + m_idx
        # If n_cnt < m_cnt: n is shorter, n changes faster
        #   local_idx = m_idx * n_cnt + n_idx
        if cluster_tile_m_cnt <= cluster_tile_n_cnt:
            # M is shorter or equal, M changes faster
            cluster_tile_m_idx = local_idx % cluster_tile_m_cnt
            cluster_tile_n_idx = local_idx // cluster_tile_m_cnt
        else:
            # N is shorter, N changes faster
            cluster_tile_n_idx = local_idx % cluster_tile_n_cnt
            cluster_tile_m_idx = local_idx // cluster_tile_n_cnt
        
        return (cluster_tile_m_idx, cluster_tile_n_idx)
    
    @dsl_user_op
    @cute.jit
    def _get_cluster_tile_counts(
        self,
        expert_idx: Int32,
        *,
        loc=None,
        ip=None,
    ) -> Tuple[Int32, Int32]:
        """Get (cluster_tile_m_cnt, cluster_tile_n_cnt) for a given expert."""
        if const_expr(self.scenario == "2Dx2D"):
            # Fixed M=hidden, N=intermediate
            cluster_tile_m_cnt = (self.hidden + self.cluster_tile_m - 1) // self.cluster_tile_m
            cluster_tile_n_cnt = (self.intermediate + self.cluster_tile_n - 1) // self.cluster_tile_n
        else:  # 2Dx3D
            # Variable M (tokens), fixed N
            tokens_i = self.offs[expert_idx]
            if expert_idx > 0:
                tokens_i = tokens_i - self.offs[expert_idx - 1]  # type: ignore[operator]
            cluster_tile_m_cnt = (
                tokens_i + self.cluster_tile_m - 1  # type: ignore[operator]
            ) // self.cluster_tile_m
            cluster_tile_n_cnt = (
                self.intermediate + self.cluster_tile_n - 1
            ) // self.cluster_tile_n
        return (cluster_tile_m_cnt, cluster_tile_n_cnt)
    
    @dsl_user_op
    @cute.jit
    def _compute_k_tile_cnt(
        self,
        expert_idx: Int32,
        *,
        loc=None,
        ip=None,
    ) -> Int32:
        """
        Compute the number of K tiles for this expert.
        
        2Dx3D: K = hidden (fixed) -> k_tile_cnt = ceil(hidden / cta_tile_k)
        2Dx2D: K = tokens_i (variable) -> k_tile_cnt = ceil(tokens_i / cta_tile_k)
        """
        if const_expr(self.scenario == "2Dx3D"):
            # K is hidden (fixed)
            return (self.hidden + self.cta_tile_k - 1) // self.cta_tile_k
        else:  # 2Dx2D
            # K is tokens_i (variable per expert)
            tokens_i = self.offs[expert_idx]
            if expert_idx > cutlass.Int32(0):
                tokens_i = tokens_i - self.offs[expert_idx - 1]  # type: ignore[operator]
            return (tokens_i + self.cta_tile_k - 1) // self.cta_tile_k  # type: ignore[return-value, operator]