[BUG] Computing result error in cutlass gemm with specfied shape

[chenhongyu2048]

when I use cutlass template to write my own gemm kernel, I meet a Internal error, even I follow the settings provided by cutlass profiler.

The full code is as below:

#include <iostream>

#include "cutlass/cutlass.h"
#include "cutlass/gemm/device/gemm.h"

#include "cutlass/util/command_line.h"
#include "cutlass/util/host_tensor.h"
#include "cutlass/util/reference/device/gemm.h"
#include "cutlass/util/reference/host/tensor_compare.h"
#include "cutlass/util/reference/host/tensor_copy.h"
#include "cutlass/util/reference/host/tensor_fill.h"
#include "cutlass/util/tensor_view_io.h"

#include "helper.h"

/////////////////////////////////////////////////////////////////////////////////////////////////

/// Result structure
struct Result
{

    double runtime_ms;
    double gflops;
    cutlass::Status status;
    cudaError_t error;
    bool passed;

    //
    // Methods
    //

    Result(
        double runtime_ms = 0,
        double gflops = 0,
        cutlass::Status status = cutlass::Status::kSuccess,
        cudaError_t error = cudaSuccess) : runtime_ms(runtime_ms), gflops(gflops), status(status), error(error), passed(true) {}
};

///////////////////////////////////////////////////////////////////////////////////////////////////

// Command line options parsing
struct Options {
    
    bool help;

    cutlass::gemm::GemmCoord problem_size;
    int batch_count;
    float alpha;
    float beta;

    bool reference_check;
    int iterations;

    Options() : help(false),
                problem_size({32, 24576, 6144}),
                batch_count(1),
                reference_check(true),
                iterations(20),
                alpha(1),
                beta() {}

    bool valid() {
        return true;
    }

    // Parses the command line
    void parse(int argc, char const **args) {

        cutlass::CommandLine cmd(argc, args);
        if (cmd.check_cmd_line_flag("help")) {
            help = true;
        }

        cmd.get_cmd_line_argument("m", problem_size.m());
        cmd.get_cmd_line_argument("n", problem_size.n());
        cmd.get_cmd_line_argument("k", problem_size.k());

        cmd.get_cmd_line_argument("alpha", alpha);
        cmd.get_cmd_line_argument("beta", beta);

        cmd.get_cmd_line_argument("iterations", iterations);
    }

    /// Prints the usage statement.
    std::ostream &print_usage(std::ostream &out) const {

        out << "14_ampere_tf32_tensorop_gemm example\n\n"
            << "This example uses the CUTLASS Library to execute TF32 tensorop GEMM computations.\n\n"
            << "Options:\n\n"
            << "  --help                      If specified, displays this usage statement.\n\n"
            << "  --m=<int>                   GEMM M dimension\n"
            << "  --n=<int>                   GEMM N dimension\n"
            << "  --k=<int>                   GEMM K dimension\n"
            << "  --alpha=<f32>               Epilogue scalar alpha\n"
            << "  --beta=<f32>                Epilogue scalar beta\n"
            << "  --iterations=<int>          Number of profiling iterations to perform.\n\n";

        out << "\nExamples:\n\n"
            << "$ ./examples/14_ampere_tf32_tensorop_gemm/14_ampere_tf32_tensorop_gemm --m=1024 --n=512 --k=1024 \\\n"
            << "     --alpha=2 --beta=0.707 \n";

        return out;
    }

    /// Compute performance in GFLOP/s
    double gflops(double runtime_s) const {
        // Number of real-valued multiply-adds
        int64_t fmas = problem_size.product() * batch_count;

        // Two flops per multiply-add
        return 2.0 * double(fmas) / double(1.0e9) / runtime_s;
    }
};

///////////////////////////////////////////////////////////////////////////////////////////////////

// The code section below describes datatype for input, output matrices and computation between
// elements in input matrices.
using ElementAccumulator = cutlass::half_t;                  // <- data type of accumulator
using ElementComputeEpilogue = ElementAccumulator; // <- data type of epilogue operations
using ElementInputA = cutlass::half_t;                       // <- data type of elements in input matrix A
using ElementInputB = cutlass::half_t;                       // <- data type of elements in input matrix B
using ElementOutput = cutlass::half_t;                       // <- data type of elements in output matrix D

// The code section below describes matrix layout of input and output matrices. Row Colume for A matrix, while Column Major for B and C matrix.
using LayoutInputA = cutlass::layout::RowMajor;
using LayoutInputB = cutlass::layout::RowMajor;
using LayoutOutput = cutlass::layout::ColumnMajor;

// This code section describes whether you want to use tensor cores or regular SIMT cores on GPU SM
using MMAOp = cutlass::arch::OpClassTensorOp;

// This code section describes CUDA SM architecture number
using SmArch = cutlass::arch::Sm80;

// This code section describes the tile size a thread block will compute
using ShapeMMAThreadBlock = cutlass::gemm::GemmShape<256, 128, 32>; // <- threadblock tile M = 128, N = 128, K = 32
// This code section describes tile size a warp will compute
using ShapeMMAWarp = cutlass::gemm::GemmShape<64, 64, 32>; // <- warp tile M = 64, N = 64, K = 32
// This code section describes the size of MMA op
using ShapeMMAOp = cutlass::gemm::GemmShape<16, 8, 8>; // <- MMA Op tile M = 16, N = 8, K = 8

// This code section describes how threadblocks are scheduled on GPU
using SwizzleThreadBlock = cutlass::gemm::threadblock::GemmIdentityThreadblockSwizzle<>;

// This code section describes the epilogue part of the kernel
using EpilogueOp = cutlass::epilogue::thread::LinearCombination<
    ElementOutput,                                    // <- data type of output matrix
    128 / cutlass::sizeof_bits<ElementOutput>::value, // <- the number of elements per vectorized
                                                      // memory access. For a byte, it's 16
                                                      // elements. This becomes the vector width of
                                                      // math instructions in the epilogue too
    ElementAccumulator,                               // <- data type of accumulator
    ElementComputeEpilogue>;                          // <- data type for alpha/beta in linear combination function

// Number of pipelines you want to use
constexpr int NumStages = 2;

using Gemm = cutlass::gemm::device::Gemm<ElementInputA,
                                         LayoutInputA,
                                         ElementInputB,
                                         LayoutInputB,
                                         ElementOutput,
                                         LayoutOutput,
                                         ElementAccumulator,
                                         MMAOp,
                                         SmArch,
                                         ShapeMMAThreadBlock,
                                         ShapeMMAWarp,
                                         ShapeMMAOp,
                                         EpilogueOp,
                                         SwizzleThreadBlock,
                                         NumStages,
                                         8,       // AlignmentA
                                         8>;      //AlignmentB

int run(Options &options) {

    // Create a tuple of problem size for matrix multiplication
    cutlass::gemm::GemmCoord problem_size = options.problem_size;

    // Initialize tensors using CUTLASS helper functions
    cutlass::HostTensor<ElementInputA, LayoutInputA> tensor_a(
        problem_size.mk()); // <- Create matrix A with dimensions M x K
    cutlass::HostTensor<ElementInputB, LayoutInputB> tensor_b(
        problem_size.kn()); // <- Create matrix B with dimensions K x N
    cutlass::HostTensor<ElementOutput, LayoutOutput> tensor_c(
        problem_size.mn()); // <- Create matrix C with dimensions M x N
    cutlass::HostTensor<ElementOutput, LayoutOutput> tensor_d(
        problem_size.mn()); // <- Create matrix D with dimensions M x N used to store output from
                            // CUTLASS kernel
    cutlass::HostTensor<ElementOutput, LayoutOutput> tensor_ref_d(
        problem_size.mn()); // <- Create matrix D with dimensions M x N used to store output from
                            // reference kernel

    // Fill input and output matrices on host using CUTLASS helper functions
    cutlass::reference::host::TensorFillRandomUniform(
        tensor_a.host_view(),
        1,
        ElementInputA(4),
        ElementInputA(-4),
        0); // <- Fill matrix A on host with uniform-distribution random data
    cutlass::reference::host::TensorFillRandomUniform(
        tensor_b.host_view(),
        1,
        ElementInputB(4),
        ElementInputB(-4),
        0); // <- Fill matrix B on host with uniform-distribution random data
    cutlass::reference::host::TensorFillRandomUniform(
        tensor_c.host_view(),
        1,
        ElementOutput(4),
        ElementOutput(-4),
        0); // <- Fill matrix C on host with uniform-distribution random data
    cutlass::reference::host::TensorFill(
        tensor_d.host_view()); // <- fill matrix D on host with zeros
    cutlass::reference::host::TensorFill(
        tensor_ref_d.host_view()); // <- fill matrix D for reference on host with zeros

    // Copy data from host to GPU
    tensor_a.sync_device();
    tensor_b.sync_device();
    tensor_c.sync_device();
    tensor_d.sync_device();
    tensor_ref_d.sync_device();

    // Initialize alpha and beta for dot product computation
    ElementComputeEpilogue alpha = ElementComputeEpilogue(options.alpha);
    ElementComputeEpilogue beta = ElementComputeEpilogue(options.beta);

    // Split K dimension into 1 partitions
    int split_k_slices = 1;

    // Create a tuple of gemm kernel arguments. This is later passed as arguments to launch
    // instantiated CUTLASS kernel
    typename Gemm::Arguments arguments{problem_size,          // <- problem size of matrix multiplication
                                       tensor_a.device_ref(), // <- reference to matrix A on device
                                       tensor_b.device_ref(), // <- reference to matrix B on device
                                       tensor_c.device_ref(), // <- reference to matrix C on device
                                       tensor_d.device_ref(), // <- reference to matrix D on device
                                       {alpha, beta},         // <- tuple of alpha and beta
                                       split_k_slices};       // <- k-dimension split factor

    // Using the arguments, query for extra workspace required for matrix multiplication computation
    size_t workspace_size = Gemm::get_workspace_size(arguments);

    // Allocate workspace memory
    cutlass::device_memory::allocation<uint8_t> workspace(workspace_size);

    // Instantiate CUTLASS kernel depending on templates
    Gemm gemm_op;

    // Check the problem size is supported or not
    cutlass::Status status = gemm_op.can_implement(arguments);
    CUTLASS_CHECK(status);

    // Initialize CUTLASS kernel with arguments and workspace pointer
    status = gemm_op.initialize(arguments, workspace.get());
    CUTLASS_CHECK(status);

    // warmup loop
    for (int iter = 0; iter < 5; ++iter) {
        // Launch initialized CUTLASS kernel
        status = gemm_op();
        CUTLASS_CHECK(status);
    }

    // Result structure
    Result result;

    // Construct events
    cudaEvent_t events[2];
    for (auto &event : events) {
        result.error = cudaEventCreate(&event);
        if (result.error != cudaSuccess) {
            std::cerr << "cudaEventCreate() failed: " << cudaGetErrorString(result.error) << std::endl;
            return -1;
        }
    }

    // Record an event at the start of a series of GEMMs
    result.error = cudaEventRecord(events[0]);
    if (result.error != cudaSuccess) {
        std::cerr << "cudaEventRecord() failed: " << cudaGetErrorString(result.error) << std::endl;
        return -1;
    }

    // Run profiling loop
    for (int iter = 0; iter < options.iterations; ++iter) {
        // Launch initialized CUTLASS kernel
        status = gemm_op();
        // CUDA_CHECK(cudaDeviceSynchronize());
        CUTLASS_CHECK(status);
    }

    // Stop profiling loop
    // Record an event when the GEMMs are complete
    result.error = cudaEventRecord(events[1]);
    if (result.error != cudaSuccess) {
        std::cerr << "cudaEventRecord() failed: " << cudaGetErrorString(result.error) << std::endl;
        return -1;
    }

    // Wait for work on the device to complete.
    result.error = cudaEventSynchronize(events[1]);
    if (result.error != cudaSuccess) {
        std::cerr << "cudaEventSynchronize() failed: " << cudaGetErrorString(result.error) << std::endl;
        return -1;
    }

    // Measure elapsed runtime
    float runtime_ms = 0;
    result.error = cudaEventElapsedTime(&runtime_ms, events[0], events[1]);
    if (result.error != cudaSuccess) {
        std::cerr << "cudaEventElapsed() failed: " << cudaGetErrorString(result.error) << std::endl;
        return -1;
    }

    // Compute average runtime and GFLOPs.
    result.runtime_ms = double(runtime_ms) / double(options.iterations);
    result.gflops = options.gflops(result.runtime_ms / 1000.0);

    // Cleanup
    for (auto event : events) {
        (void)cudaEventDestroy(event);
    }

    // Create instantiation for device reference gemm kernel
    cutlass::reference::device::Gemm<ElementInputA,
                                     LayoutInputA,
                                     ElementInputB,
                                     LayoutInputB,
                                     ElementOutput,
                                     LayoutOutput,
                                     ElementComputeEpilogue,
                                     ElementComputeEpilogue> gemm_device;

    // Launch device reference gemm kernel
    gemm_device(problem_size,
                alpha,
                tensor_a.device_ref(),
                tensor_b.device_ref(),
                beta,
                tensor_c.device_ref(),
                tensor_ref_d.device_ref());

    // Wait for kernels to finish
    CUDA_CHECK(cudaDeviceSynchronize());

    // Copy output data from CUTLASS and reference kernel to host for comparison
    tensor_d.sync_host();
    tensor_ref_d.sync_host();

    // Check if output from CUTLASS kernel and reference kernel are equal or not
    bool passed = cutlass::reference::host::TensorEquals(
        tensor_d.host_view(),
        tensor_ref_d.host_view());

    std::cout << "Runtime: " << result.runtime_ms * 1000 << " us" << std::endl;
    std::cout << " GFLOPs: " << result.gflops << std::endl;

    // if (passed) {
    //     std::cout << "Runtime: " << result.runtime_ms * 1000 << " us" << std::endl;
    //     std::cout << " GFLOPs: " << result.gflops << std::endl;
    // }

    std::cout << (passed ? "Passed" : "Failed") << std::endl;

    return (passed ? 0 : -1);
}

int main(int argc, const char **argv) {
    bool notSupported = false;

    // Ampere Tensor Core operations exposed with mma.sync and ldmatrix are first available
    // in CUDA 11.0.
    // CUTLASS must be compiled with CUDA 11.0 Toolkit to run these examples.
    if (!(__CUDACC_VER_MAJOR__ >= 11)) {
        std::cerr << "Ampere Tensor Core operations must be compiled with CUDA 11.0 Toolkit or later." << std::endl;
        notSupported = true;
    }

    cudaDeviceProp props;
    cudaError_t error = cudaGetDeviceProperties(&props, 0);
    if (error != cudaSuccess) {
        std::cerr << "cudaGetDeviceProperties() returned an error: " << cudaGetErrorString(error) << std::endl;
        return -1;
    }

    if (!((props.major * 10 + props.minor) >= 80)) {
        std::cerr << "Ampere Tensor Core operations must be run on a machine with compute capability at least 80."
                  << std::endl;
        notSupported = true;
    }

    if (notSupported) {
        // Returning zero so this test passes on older Toolkits. Its actions are no-op.
        return 0;
    }

    std::cout << "Device Name: " << props.name << std::endl;
    std::cout << "Number of Streaming Multiprocessors: " << props.multiProcessorCount << std::endl;

    Options options;
    options.parse(argc, argv);

    if (options.help) {
        options.print_usage(std::cout) << std::endl;
        return 0;
    }

    printf("%d x %d x %d Half tensor op Matrix Multiply\n", options.problem_size.m(), options.problem_size.n(), options.problem_size.k());

    if (!options.valid()) {
        std::cerr << "Invalid problem." << std::endl;
        return -1;
    }

    return run(options);
}

The above setting is provided by cutlass profiler:

Problem ID: 1

        Provider: CUTLASS
   OperationKind: gemm
       Operation: cutlass_tensorop_h1688gemm_256x128_32x2_tt_align8

          Status: Success
    Verification: ON
     Disposition: Passed

reference_device: Passed
          cuBLAS: Not run
           cuDNN: Not run

       Arguments: --gemm_kind=universal --m=32 --n=24576 --k=6144 --A=f16:row --B=f16:row --C=f16:column --D=f16:column  \
                  --alpha=1 --beta=0 --split_k_mode=serial --split_k_slices=1 --batch_count=1 --raster_order=heuristic  \
                  --swizzle_size=1 --op_class=tensorop --accum=f16 --cta_m=256 --cta_n=128 --cta_k=32 --cluster_m=1 --cluster_n=1  \
                  --cluster_k=1 --stages=2 --warps_m=4 --warps_n=2 --warps_k=1 --inst_m=16 --inst_n=8 --inst_k=8 --min_cc=75  \
                  --max_cc=1024

           Bytes: 303955968  bytes
           FLOPs: 9665249280  flops
           FLOPs/Byte: 31

         Runtime: 0.328755  ms
          Memory: 861.069 GiB/s

            Math: 29399.5 GFLOP/s

I compiled it with nvcc -std=c++17 -arch=sm_80 -I/xxx/third_party/cutlass/include -I/xxx/third_party/cutlass/tools/util/include -I/xxx/third_party/cutlass/tools/library/include -I/xxx/third_party/cutlass/examples/common -lcublas ./cutlass_gemm.cu --expt-relaxed-constexpr -o cutlass_gemm_example. I use cuda12.6 and RTX 6000 ada GPU.
I'd like to know if this is an issue with the way I'm using it?

[chenhongyu2048]

UPDATE: the running result: will not report error (computation is finished), but cutlass::reference::host::TensorEquals failed

[chenhongyu2048]

UPDATE: the running result: will not report error (computation is finished), but cutlass::reference::host::TensorEquals failed

Maybe such an error is an accuracy issue?

[chenhongyu2048]

After further debugging, we found that this error was caused by the difference between the calculation result and the tensor_ref_d in some of the values. We've added the following code:

ElementOutput sum = (ElementOutput)0;
ElementOutput *d_ptr = tensor_d.host_data();
ElementOutput *ref_d_ptr = tensor_ref_d.host_data();
for (int i = 0; i < 32 * 12288; ++i) {
    sum += *(d_ptr+i) - *(ref_d_ptr+i);
    if (*(d_ptr+i) - *(ref_d_ptr+i) != 0) {
        std::cout<<i<<" "<<*(d_ptr+i) - *(ref_d_ptr+i)<<std::endl;
    }
}
std::cout << sum << std::endl;

and got the following result: when i=60390, print -4, which is the differnece between *(d_ptr+i) and *(ref_d_ptr+i).

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