[Openmp-dev] GPU Target Offloading - Cannot Find GPU

[Jonas Hahnfeld via Openmp-dev]

Hi,

On 2019-01-29 17:51, Qiongsi Wu via Openmp-dev wrote:
> Hi everyone!
> 
> I am following Jonas Hahnfeld’s blog post
> (https://www.hahnjo.de/blog/2018/10/08/clang-7.0-openmp-offloading-nvidia.html)
> to build clang to test some simple target offloading workloads.
> 
> The complete code can be found at the end.
> 
> I tried clang 7.0.1 and llvm trunk (9.0.0). omp_get_num_devices()
> returned 0 for both compilers although the server I am running this on
> has Quadro P4000 on it. As an attempt to fix the issue, I added
> compute compatibility 61 and set it to default. This did not help.
> 
> Additionally, the binary built by trunk cannot even offload to CPU
> targets, reporting error
> 
> "Libomptarget fatal error 1: default offloading policy must switched
> to mandatory or disabled”
> 
> May I get some help from the community on what to look into to get
> this microbenchmark to run on the GPU?
> 
> Thanks!
> 
> ######################################################################################################
> 
> 
> #include <stdio.h>
> #include <stdlib.h>
> #include <time.h>
> #include <omp.h>
> 
> #define VALUE_TYPE double
> #define ARR_SIZE  128 * 1024 * 1024
> 
> struct timespec timespec_diff(struct timespec t1, struct timespec t2)
> {
>     struct timespec diff;
> 
>     diff.tv_nsec = t1.tv_nsec - t2.tv_nsec;
>     diff.tv_sec = t1.tv_sec - t2.tv_sec;
>     if (diff.tv_nsec < 0) {
>         diff.tv_nsec += 1000000000;
>         diff.tv_sec -= 1;
>     }
> 
>     return diff;
> }
> 
> double timespec_to_sec(struct timespec t) {
>     double sec = (double)t.tv_sec;
>     double nsec = (double)t.tv_nsec;
>     return sec + nsec * 1E-9;
> }
> 
> void gen_rand_number(VALUE_TYPE *arr, int size) {
>     for (int i = 0; i < size; i++) {
>         arr[i] = (VALUE_TYPE)rand();
>     }
> }
> 
> void cpu_add(VALUE_TYPE *out, VALUE_TYPE *in_1, VALUE_TYPE *in_2, int
> size) {
>     for (int i = 0; i < size; i++) {
>         out[i] = in_1[i] + in_2[i];
>     }
> }
> 
> void omp_cpu_add(VALUE_TYPE *out, VALUE_TYPE *in_1, VALUE_TYPE *in_2,
> int size) {
> #pragma omp parallel for
>     for (int i = 0; i < size; i++) {
>         out[i] = in_1[i] + in_2[i];
>     }
> }
> 
> void omp_gpu_add(VALUE_TYPE *out, VALUE_TYPE *in_1, VALUE_TYPE *in_2,
> int size) {
> #pragma omp target map(to:in_1, in_2) map(from:out)

I think the compiler will have trouble to correctly map / transfer the 
arrays here. Can you try specifying array sections?
Should be as easy as "map(to:in_1[0:size], in_2[0:size]) 
map(from:out[0:size])"

Hope this helps and fixes the problem :)
Jonas

> #pragma omp teams
> #pragma omp distribute parallel for
>     for (int i = 0; i < size; i++) {
>         out[i] = in_1[i] + in_2[i];
>     }
> }
> 
> int main() {
>     VALUE_TYPE *a = malloc(sizeof(VALUE_TYPE) * ARR_SIZE);
>     VALUE_TYPE *b = malloc(sizeof(VALUE_TYPE) * ARR_SIZE);
>     VALUE_TYPE *c_1 = malloc(sizeof(VALUE_TYPE) * ARR_SIZE);
>     VALUE_TYPE *c_2 = malloc(sizeof(VALUE_TYPE) * ARR_SIZE);
>     VALUE_TYPE *c_3 = malloc(sizeof(VALUE_TYPE) * ARR_SIZE);
> 
>     struct timespec start, end, diff;
> 
>     gen_rand_number(a, ARR_SIZE);
>     gen_rand_number(b, ARR_SIZE);
> 
>     printf("number of omp devices %d\n", omp_get_num_devices());
>     printf("number of omp teams %d\n", omp_get_num_teams());
> 
>     clock_gettime(CLOCK_MONOTONIC, &start);
>     cpu_add(c_1, a, b, ARR_SIZE);
>     clock_gettime(CLOCK_MONOTONIC, &end);
>     printf("CPU took %f seconds. \n",
> timespec_to_sec(timespec_diff(end, start)));
> 
>     clock_gettime(CLOCK_MONOTONIC, &start);
>     omp_cpu_add(c_2, a, b, ARR_SIZE);
>     clock_gettime(CLOCK_MONOTONIC, &end);
>     printf("CPU omp took %f seconds. \n",
> timespec_to_sec(timespec_diff(end, start)));
> 
>     clock_gettime(CLOCK_MONOTONIC, &start);
>     for (int i = 0; i < 100; i++) {
>         omp_gpu_add(c_3, a, b, ARR_SIZE);
>     }
>     clock_gettime(CLOCK_MONOTONIC, &end);
>     printf("GPU omp offload took %f seconds. \n",
> timespec_to_sec(timespec_diff(end, start)) / 100.0);
> }
> 
> ######################################################################################################
> 
> 
>  Sincerely,
>  Qiongsi
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