Question

我在Metal中结合Swift实现多核函数时遇到了问题。

我的目标是在图像上实现逐块DCT变换。 DCT通过两次矩阵乘法实现。

J = H * I * H ^ -1

以下代码显示了内核函数本身以及swift代码中使用的调用。如果我单独运行每个内核函数它可以工作，但我无法设法将写入缓冲区从第一个内核函数移交给第二个函数。因此，第二个函数总是返回一个只填充0的缓冲区。

所有图像输入和输出缓冲区都是400x400大的RGB（每个组件16位整数）。矩阵是8x8 16位整数。

是否需要一个特殊的命令来同步不同内核函数的缓冲区读写访问？或者我做错了什么？

感谢您的帮助

shaders.metal

struct Image3D16{
    short data[400][400][3];
};

struct Matrix{
    short data[8 * 8];
};

kernel void dct1(device Image3D16 *inputImage [[buffer(0)]],
            device Image3D16 *outputImage [[buffer(1)]],
            device Matrix *mult [[buffer(2)]],
            uint2 gid [[thread_position_in_grid]],
            uint2 tid [[thread_position_in_threadgroup]]){

    int red = 0, green = 0, blue = 0;

    for(int x=0;x<8;x++){
        short r = inputImage->data[gid.x-tid.x + x][gid.y][0];
        short g = inputImage->data[gid.x-tid.x + x][gid.y][1];
        short b = inputImage->data[gid.x-tid.x + x][gid.y][2];

        red += r * mult->data[tid.x*8 + x];
        green += g * mult->data[tid.x*8 + x];
        blue += b * mult->data[tid.x*8 + x];
    }

    outputImage->data[gid.x][gid.y][0] = red;
    outputImage->data[gid.x][gid.y][1] = green;
    outputImage->data[gid.x][gid.y][2] = blue;
}

kernel void dct2(device Image3D16 *inputImage [[buffer(0)]],
             device Image3D16 *outputImage [[buffer(1)]],
             device Matrix *mult [[buffer(2)]],
             uint2 gid [[thread_position_in_grid]],
             uint2 tid [[thread_position_in_threadgroup]]){

    int red = 0, green = 0, blue = 0;
    for(int y=0;y<8;y++){
        short r = inputImage->data[gid.x][gid.y-tid.y + y][0];
        short g = inputImage->data[gid.x][gid.y-tid.y + y][1];
        short b = inputImage->data[gid.x][gid.y-tid.y + y][2];

        red += r * mult->data[tid.y*8 + y];
        green += g * mult->data[tid.y*8 + y];
        blue += b * mult->data[tid.y*8 + y];
    }

    outputImage->data[gid.x][gid.y][0] = red;
    outputImage->data[gid.x][gid.y][1] = green;
    outputImage->data[gid.x][gid.y][2] = blue;
}

ViewController.swift

...

let commandBuffer = commandQueue.commandBuffer()
let computeEncoder1 = commandBuffer.computeCommandEncoder()
computeEncoder1.setComputePipelineState(computeDCT1)
computeEncoder1.setBuffer(input, offset: 0, atIndex: 0)
computeEncoder1.setBuffer(tmpBuffer3D1, offset: 0, atIndex: 1)
computeEncoder1.setBuffer(dctMatrix1, offset: 0, atIndex: 2)
computeEncoder1.dispatchThreadgroups(blocks, threadsPerThreadgroup: dctSize)
computeEncoder1.endEncoding()

let computeEncoder2 = commandBuffer.computeCommandEncoder()
computeEncoder2.setComputePipelineState(computeDCT2)
computeEncoder2.setBuffer(tmpBuffer3D1, offset: 0, atIndex: 0)
computeEncoder2.setBuffer(output, offset: 0, atIndex: 1)
computeEncoder2.setBuffer(dctMatrix2, offset: 0, atIndex: 2)
computeEncoder2.dispatchThreadgroups(blocks, threadsPerThreadgroup: dctSize)
computeEncoder2.endEncoding()

commandBuffer.commit()
commandBuffer.waitUntilCompleted()

Answer 1

我发现了错误。我的内核函数试图在其分配的内存之外读取。然后，金属接口的反应是停止在命令缓冲区中执行所有后续命令。因此，输出始终为零，因为计算从未完成。应用程序的GPU使用率下降，可用于检测错误。

ios metal：在一个命令缓冲区中进行多个内核调用

1 个答案: