utils_gmem.cuh

//    Copyright 2024 FP6-LLM authors
//
//    Licensed under the Apache License, Version 2.0 (the "License");
//    you may not use this file except in compliance with the License.
//    You may obtain a copy of the License at
//
//        http://www.apache.org/licenses/LICENSE-2.0
//
//    Unless required by applicable law or agreed to in writing, software
//    distributed under the License is distributed on an "AS IS" BASIS,
//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//    See the License for the specific language governing permissions and
//    limitations under the License.
// 
// This file is modified from https://github.com/usyd-fsalab/fp6_llm/blob/ce76774bcfc26b325c1b558abcf1935026d9abbc/fp6_llm/csrc/include/utils_gmem.cuh

#ifndef UTILS_GMEM_CUH
#define UTILS_GMEM_CUH

#include <assert.h>
#include "configs.h"
#include "ptx_cp.async.cuh"

/* 
 * Copying A1/A2 from global memory to shared memory.
 * Usually 1024 or 2048 Bytes
 */
template<int SMEM_SIZE_IN_BYTES_PER_WARP>
__device__ __forceinline__ void CopyFromGlobalToShared_A(uint32_t* SPTR, 
                                                        const uint4* GPTR,
                                                        bool pred_guard = true) {
    #ifdef DEBUG_MODE
        static_assert(SMEM_SIZE_IN_BYTES_PER_WARP/WARP_SIZE % 16 == 0);
    #endif
    int lane_id      = threadIdx.x % WARP_SIZE;
    half* SPTR_HALF = reinterpret_cast<half*>(SPTR);
    const half* GPTR_HALF = reinterpret_cast<const half*>(GPTR);
    SPTR_HALF += lane_id*8;
    GPTR_HALF += lane_id*8;
    #pragma unroll
    for(int i=0; i<SMEM_SIZE_IN_BYTES_PER_WARP/WARP_SIZE/16; i++) {
        cp_async<16>( SPTR_HALF, GPTR_HALF, pred_guard);
        SPTR_HALF += 256;   // Forward 512 Bytes
        GPTR_HALF += 256;   // Forward 512 Bytes
    }

}

/* 
 * Copying 64 Quant Scales (FP16) from global memory to shared memory.
 */
__device__ __forceinline__ void CopyFromGlobalToShared_Scales(half* SPTR_QuantScales,
                                                              const half* GPTR_A_Scales) {
    int lane_id         = threadIdx.x % WARP_SIZE;
    int Offset_Shared   = lane_id*2; 
    int Offset_Global   = lane_id/4 + (lane_id%4)*16;
    for(int i=0; i<2; i++)  SPTR_QuantScales[Offset_Shared+i] = GPTR_A_Scales[Offset_Global+i*8];
}

// MODIFICATION NOTE: to support MSVC, half __restrict__ (*SharedPTR)[WARP_K+PADDING_SHARED_MEM_FOR_B_8] is changed to below.
/* 
 * (1) Copying X  rows * 64 columns of FP16 values, originally in row    major
 * (2) Copying 64 rows * X  columns of FP16 values, originally in column major
 * 16 Bytes per thread -> 512 Bytes per WARP = 4 line per WARP = 1 line per 8 Threads
 */
template<int MaxNumOfLinesToCopy, int BLOCK_WARPS>
__device__ __forceinline__ void CopyFromGlobalToShared(half (* __restrict__ SharedPTR)[WARP_K+PADDING_SHARED_MEM_FOR_B_8],
                                                       const half*          GlobalPTR,
                                                       const int            GlobalStride,
                                                       const int            NumOfLinesLeft,        // To support arbitrary N dimensions.
                                                       bool                 Pred = true) {
    // static parameters: 1 Group (8 Threads) can copy 1 line (64 FP16) each time
    const int NumOfThreads  = BLOCK_WARPS * WARP_SIZE;
    const int NumOfGroups   = NumOfThreads / 8; 
    const int MaxIteration  = (MaxNumOfLinesToCopy-1) / NumOfGroups + 1;
    // runtime variables   
    const int line_id       = threadIdx.x / 8;
    const int line_offset   = (threadIdx.x%8) * 8;
    // PTR for source global memory and target shared memory
    GlobalPTR += line_id * GlobalStride + line_offset;
    SharedPTR += line_id;
    #pragma unroll
    for (int i = 0; i < MaxIteration; i++) {
        bool AsyncCopyPred = (line_id+i*NumOfGroups) < NumOfLinesLeft && Pred;
        cp_async<16>( &(*SharedPTR)[line_offset], GlobalPTR, AsyncCopyPred);
        //
        GlobalPTR += NumOfGroups * GlobalStride;
        SharedPTR += NumOfGroups;
    }
}

#endif