推力:如何直接控制算法调用的执行? [英] Thrust: How to directly control where an algorithm invocation executes?
问题描述
以下代码没有可能导致其在CPU或GPU上运行的信息。我不知道reduce操作在哪里执行?
The following code has no information that may lead it to run at CPU or GPU. I wonder where is the "reduce" operation executed?
#include <thrust/iterator/counting_iterator.h>
...
// create iterators
thrust::counting_iterator<int> first(10);
thrust::counting_iterator<int> last = first + 3;
first[0] // returns 10
first[1] // returns 11
first[100] // returns 110
// sum of [first, last)
thrust::reduce(first, last); // returns 33 (i.e. 10 + 11 + 12)
此外,
thrust::transform_reduce(
thrust::counting_iterator<unsigned int>(0),
thrust::counting_iterator<unsigned int>(N),
MyOperation(data), 0 ,thrust::plus<unsigned int>())
即使数据被定义为thrust :: host_vector,这个函数试图在GPU上执行(编译器给出相关的错误,因为文件名以.cpp结尾)。我如何让代码在CPU上运行。或者我应该寻找另一种方式来执行相同的操作,例如。不使用counting_iterator?
Even though data is defined as thrust::host_vector, this function tries to be executed at GPU (compiler gives related errors, because the filename ends with .cpp). How may I make the code to run at CPU. Or should I look for another way to perform the same operation, e.g. not using counting_iterator?
推荐答案
默认情况下,像这样的算法调用在设备后端执行。
By default, algorithm invocations like this execute on the device backend (i.e., the GPU in your case).
如果您使用的是Thrust 1.7或更高版本,请使用 thrust :: host
执行策略强制算法调用以在主机(即CPU)上执行:
If you're using Thrust 1.7 or better, use the thrust::host
execution policy to force an algorithm invocation to execute on the host (i.e., the CPU):
#include <thrust/execution_policy.h>
...
thrust::reduce(thrust::host, first, last);
...
thrust::transform_reduce(thrust::host,
first,
last,
MyOperation(data),
0,
thrust::plus<unsigned int>());
如果您使用的是Thrust 1.6,您可以通过 retag
取得现有的迭代器:
If you're using Thrust 1.6, you can retarget the invocations to the host by retag
ging an existing iterator:
#include <thrust/iterator/retag.h>
...
thrust::reduce(thrust::retag<thrust::host_system_tag>(first),
thrust::retag<thrust::host_system_tag>(last));
...
thrust::transform_reduce(thrust::retag<thrust::host_system_tag>(first),
thrust::retag<thrust::host_system_tag>(last),
MyOperation(data),
0,
thrust::plus<unsigned int>());
如果您使用的是1.6版之前的Thrust版本,您需要传递 host_space_tag
至 counting_iterator
作为模板参数:
If you're using an older version of Thrust prior to 1.6, you need to pass host_space_tag
to counting_iterator
as a template parameter:
thrust::reduce(thrust::counting_iterator<unsigned int, thrust::host_space_tag>(0),
thrust::counting_iterator<unsigned int, thrust::host_space_tag>(N));
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