将数字添加到数组值时，由于执行期间发生错误，命令缓冲区的Swift Metal Shader执行被中止

Question

I'm trying some very simple algorithm using metal GPU acceleration to calculate some values in an array. The shader throws an error under some conditions I will explain. Error: Execution of the command buffer was aborted due to an error during execution. Ignored (for causing prior/excessive GPU errors) (IOAF code 4)

The shader only throws this error when adding a value to the existing value at an index of the array. Example:

This will not cause an error:

    kernel void shader (device int *wPointsIntensity [[buffer(0)]],
                const device uint *wPointsXCoord [[buffer(1)]],
                const device uint *wPointsYCoord [[buffer(2)]],
                device float *pixelSignalIntensity [[buffer(3)]],
                device float *pixelDistance [[buffer(4)]],
                const device uint& noOfPoints [[ buffer(5) ]],
                const device uint& width [[ buffer(6) ]],
                const device uint& height [[ buffer(7) ]],
                uint id [[ thread_position_in_grid ]]) {

//this does not throw error
for (uint wpIndex = 0; wpIndex < noOfPoints; wpIndex++) {
    for (uint heightIndex = 0; heightIndex < height; heightIndex++) {
        for (uint widthIndex = 0; widthIndex < width; widthIndex++) {

            uint pixelIndex = heightIndex * width + widthIndex;
            pixelDistance[pixelIndex] = float(pixelIndex);
            pixelSignalIntensity[pixelIndex] = float(pixelIndex);
}}}}

While if you change

pixelDistance[pixelIndex] = float(pixelIndex); with

pixelDistance[pixelIndex] += float(pixelIndex);

It will throw an error.

Here is the swift code:

var wPointsValues = [Int32](repeating:0, count: wPoints.count)
var wPointsXLocations = [Int32](repeating:0, count: wPoints.count)
var wPointsYLocations = [Int32](repeating:0, count: wPoints.count)
        for i in 0..<wPoints.count {
            wPointsValues[i] = Int32(wPoints[i].signalIntensity)
            wPointsXLocations[i] = Int32(wPoints[i].location.x)
            wPointsYLocations[i] = Int32(wPoints[i].location.y)
        }

        var numberOfWPoints:Int32 = Int32(wPoints.count)
        var int32Width = Int32(width)
        var int32Height = Int32(height)

        //output arrays

        let numberOfResults = wPoints.count * Int(width) * Int(height)
        var wPointsSignalIntensity = [Float32](repeating:0.0, count: numberOfResults)
        var wPointsDistance = [Float32](repeating:0.0, count: numberOfResults)


        //local variables
        var signalDensity:[Float32] = [Float32](repeating:0.0, count: numberOfResults)
        var signalDistance:[Float32] = [Float32](repeating:0.0, count: numberOfResults)

            //create input buffers
            let inWPointSignalValues = device.makeBuffer(bytes: wPointsValues, length: (MemoryLayout<Int32>.stride * wPoints.count), options: [])
            let inWPointXCoordBuffer = device.makeBuffer(bytes: wPointsXLocations, length: (MemoryLayout<Int32>.stride * wPoints.count), options: [])
            let inWPointYCoordBuffer = device.makeBuffer(bytes: wPointsYLocations, length: (MemoryLayout<Int32>.stride * wPoints.count), options: [])

            //create putput buffers
            let outPixelSignalIntensityBuffer = device.makeBuffer(bytes: wPointsSignalIntensity, length: (MemoryLayout<Float32>.stride * numberOfResults), options: [])
            let outPixelDistanceBuffer = device.makeBuffer(bytes: wPointsDistance, length: (MemoryLayout<Float32>.stride * numberOfResults), options: [])

            let commandBuffer = (mtlCommmandQueue?.makeCommandBuffer())!
            let computeCommandEncoder = (commandBuffer.makeComputeCommandEncoder())!
            computeCommandEncoder.setComputePipelineState(mtlComputePipelineFilter!)
            //set input buffers
            computeCommandEncoder.setBuffer(inWPointSignalValues, offset: 0, index: 0)
            computeCommandEncoder.setBuffer(inWPointXCoordBuffer, offset: 0, index: 1)
            computeCommandEncoder.setBuffer(inWPointYCoordBuffer, offset: 0, index: 2)

            //set output buffers
            computeCommandEncoder.setBuffer(outPixelSignalIntensityBuffer, offset: 0, index: 3)
            computeCommandEncoder.setBuffer(outPixelDistanceBuffer, offset: 0, index: 4)

            //set constants
            computeCommandEncoder.setBytes(&numberOfWPoints, length: MemoryLayout<Int32>.stride, index: 5)
            computeCommandEncoder.setBytes(&int32Width, length: MemoryLayout<Int32>.stride, index: 6)
            computeCommandEncoder.setBytes(&int32Height, length: MemoryLayout<Int32>.stride, index: 7)


            let threadsPerGroup = MTLSize(width:2,height:2,depth:2)
            let numThreadgroups = MTLSize(width:2, height:2, depth:2)
            computeCommandEncoder.dispatchThreadgroups(numThreadgroups, threadsPerThreadgroup: threadsPerGroup)

            let endBufferAllocation = mach_absolute_time()

            print("time for creating and setting buffert: time: \(Double(endBufferAllocation - start) / Double(NSEC_PER_SEC))")
            computeCommandEncoder.endEncoding()

            commandBuffer.commit()
            commandBuffer.waitUntilCompleted()
            let allComplete = mach_absolute_time()
        self.signalDistance = (outPixelDistanceBuffer?.contents())!
        self.signalDensity = (outPixelSignalIntensityBuffer?.contents())!

Answer 1

I had this issue for ages and program crashed intermittently. It turned out that I was accessing memory in the kernel that had not been allocated by the buffer. In the kernel I was doing a for loop 0..<5 (ie output 5 values for each thread) but had not divided the num_threads by 5.

When it didn't crash it was giving the correct answer and no errors except " Execution of the command buffer was aborted due to an error during execution. Caused GPU Hang Error (IOAF code 3)" were ever thrown.