$ cat t503.cu
#include <stdio.h>

#include <thrust/host_vector.h>
#include <thrust/device_vector.h>
#include <thrust/inner_product.h>
#include <thrust/complex.h>
#include <thrust/execution_policy.h>

int main(int argc, char **argv)
{
    int vec_size = atoi(argv[1]);
    int iterations = atoi(argv[2]);

    float milliseconds = 0;

    cudaEvent_t start, stop;
    cudaEventCreate(&start);
    cudaEventCreate(&stop);

    thrust::host_vector< thrust::complex<float> > host_x( vec_size );
    thrust::generate(host_x.begin(), host_x.end(), rand);

    thrust::host_vector< thrust::complex<float> > host_y( vec_size );
    thrust::generate(host_y.begin(), host_y.end(), rand);

    printf("vector size = %lu bytes\n", vec_size * sizeof(thrust::complex<float>));

    cudaEventRecord(start);

    thrust::device_vector< thrust::complex<float> > device_x = host_x;
    thrust::device_vector< thrust::complex<float> > device_y = host_y;
    cudaEventRecord(stop);

    cudaEventSynchronize(stop);
    cudaEventElapsedTime(&milliseconds, start, stop);

    printf("copy (device)\t\t%f ms\n", milliseconds);

    cudaEventRecord(start);

    for(int i = 0; i < iterations; ++i)
    {
        thrust::inner_product(thrust::cuda::par, device_x.begin(), device_x.end(), device_y.begin(), thrust::complex<float>(0.0f,0.0f) );
    }

    cudaEventRecord(stop);

    cudaEventSynchronize(stop);
    cudaEventElapsedTime(&milliseconds, start, stop);

    printf("inner_product (device)\t%f ms\n", milliseconds/iterations);

    cudaEventRecord(start);

    for(int i = 0; i < iterations; ++i)
    {
        thrust::inner_product(thrust::host, host_x.begin(), host_x.end(), host_y.begin(), thrust::complex<float>(0.0f,0.0f) );
    }

    cudaEventRecord(stop);

    cudaEventSynchronize(stop);
    cudaEventElapsedTime(&milliseconds, start, stop);

    printf("inner_product (host)\t%f ms\n", milliseconds/iterations);

    return 0;
}
$ nvcc -O3 -arch=sm_20 -o t503 t503.cu
$ ./t503 3100000 1000
vector size = 24800000 bytes
copy (device)           25.308224 ms
inner_product (device)  2.992532 ms
inner_product (host)    30.961256 ms
$