内存对象OpenCL的基地址 [英] Base Address of Memory Object OpenCL

问题描述

我想使用 OpenCL 在GPU上遍历一棵树，因此我将树组装在主机上的连续块中，并更改所有指针的地址，以便在设备上保持一致，如下所示:

I want to traverse a tree at GPU with OpenCL, so i assemble the tree in a contiguous block at host and i change the addresses of all pointers so as to be consistent at device as follows:

TreeAddressDevice =(size_t)BaseAddressDevice +((size_t)TreeAddressHost-(size_t)BaseAddressHost);

我要内存缓冲区的基地址: 在主机上，我为缓冲区分配内存，如下所示: cl_mem tree_d = clCreateBuffer(...);

I want the base address of the memory buffer: At host i allocate memory for the buffer, as follows: cl_mem tree_d = clCreateBuffer(...);

问题在于cl_mems是跟踪数据内部表示形式的对象.从技术上讲，它们是指向对象的指针，但它们不是指向数据的指针.从内核内部访问cl_mem的唯一方法是通过setKernelArgs将其作为参数传递.

The problem is that cl_mems are objects that track an internal representation of the data. Technically they're pointers to an object, but they are not pointers to the data. The only way to access a cl_mem from within a kernel is to pass it in as an argument via setKernelArgs.

此处

Here http://www.proxya.net/browse.php?u=%3A%2F%2Fwww.khronos.org%2Fmessage_boards%2Fviewtopic.php%3Ff%3D37%26amp%3Bt%3D2900&b=28 i found the following solution, but it doesnot work:

__kernel void getPtr( __global void *ptr, __global void *out )

    {
    *out = ptr;
    }

可以如下调用

代码:

...

    cl_mem auxBuf = clCreateBuffer( context, CL_MEM_READ_WRITE, sizeof(void*), NULL, NULL );
    void *gpuPtr;

    clSetKernelArg( getterKernel, 0, sizeof(cl_mem), &myBuf );
    clSetKernelArg( getterKernel, 1, sizeof(cl_mem), &auxBuf );
    clEnqueueTask( commandQueue, getterKernel, 0, NULL, NULL );
    clEnqueueReadBuffer( commandQueue, auxBuf, CL_TRUE, 0, sizeof(void*), &gpuPtr, 0, NULL, NULL );

    clReleaseMemObject(auxBuf);

...

现在，"gpuPtr"应该包含GPU内存空间中"myBuf"开头的地址.

Now "gpuPtr" should contain the address of the beginning of "myBuf" in GPU memory space.

解决方案很明显，我找不到它?创建缓冲区时如何获取指向设备内存的指针?

The solution is obvious and i can't find it? How can I get back a pointer to device memory when creating buffers?

推荐答案

这是因为在OpenCL模型中，主机内存和设备内存是不相交的.设备内存中的指针在主机上将没有任何意义.

It's because in the OpenCL model, host memory and device memory are disjoint. A pointer in device memory will have no meaning on the host.

您可以使用clEnqueueMapBuffer将设备缓冲区映射到主机内存.映射会将设备同步到主机，而取消映射会将主机重新同步到设备.

You can map a device buffer to host memory using clEnqueueMapBuffer. The mapping will synchronize device to host, and unmapping will synchronize back host to device.

更新.正如您在注释中解释的那样，您希望将树结构发送到GPU.一种解决方案是将所有树节点存储在数组中，用数组中的索引替换指向节点的指针.

Update. As you explain in the comments, you want to send a tree structure to the GPU. One solution would be to store all tree nodes inside an array, replacing pointers to nodes with indices in the array.

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