[Openmp-dev] Target construct not offloading to GPU

Cristobal Ortega via Openmp-dev openmp-dev at lists.llvm.org
Fri Oct 5 06:09:00 PDT 2018


I've been trying to compile a program (source code is attached) that 
offloads to a NVIDIA V-100 GPU with LLVM 7.0 and clang 7.0.

It seems that the program is successfully compiled, yet nvprof reports 
that "no kernels were profiled".
The application seems that is running on the CPU (as "top" command 
reports a high usage of CPUs).

Compilation line that I used:
clang -v  -o openmp_offload openmp_offload.c -O3 -fopenmp=libomp 

Output after executing the binary:
==74802== NVPROF is profiling process 74802, command: ./openmp_offload 
10 10 10000 1
Number of processors:     160
Number of devices:        4
Default device:           0
Is initial device:        1
==74802== Profiling application: ./openmp_offload 10 10 10000 1
==74802== Profiling result:
No kernels were profiled.
             Type  Time(%)      Time     Calls       Avg Min       Max  Name
       API calls:   99.99%  311.50ms         1  311.50ms  311.50ms 
311.50ms  cuCtxCreate
                     0.00%  11.462us         4  2.8650us  1.1450us 
6.2010us  cuDeviceGetPCIBusId
                     0.00%  5.4850us         5  1.0970us     387ns 
3.7770us  cuDeviceGet
                     0.00%  4.8070us        12     400ns     232ns 
1.0350us  cuDeviceGetAttribute
                     0.00%  1.4360us         3     478ns 384ns     
640ns  cuDeviceGetCount

When compiled with GCC, the application does the offloading to the GPU.

clang information:
$ clang -v
Version 6
Version >= 90 selected
libdevice.10.bc exists
clang version 7.0.0 (tags/RELEASE_700/final)
Target: powerpc64le-unknown-linux-gnu
Thread model: posix
InstalledDir: /gpfs/projects/bsc18/bsc18833/pkg/clang/7.0.0/bin
Found candidate GCC installation: 
Selected GCC installation: 
Candidate multilib: .;@m64
Selected multilib: .;@m64
Found CUDA installation: /usr/local/cuda-9.2, version 9.2

Hopefully somebody has an idea on what's going on here.
If you need any more information to find the issue, let me know.
Thank you.


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