Re: nvptx: 'cuDeviceGetCount' failure is fatal

[Tobias Burnus <tburnus@baylibre.com>]

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Hi Thomas,

Thomas Schwinge wrote:
>> /* Return the number of GCN devices on the system. */  
>>   int
>> -GOMP_OFFLOAD_get_num_devices (void)
>> +GOMP_OFFLOAD_get_num_devices (unsigned int omp_requires_mask)
>>   {
>>     if (!init_hsa_context ())
>>       return 0;
>> +  /* Return -1 if no omp_requires_mask cannot be fulfilled but
>> +     devices were present.  */
>> +  if (hsa_context.agent_count > 0 && omp_requires_mask != 0)
>> +    return -1;
>>     return hsa_context.agent_count;
>>   }
...
> OK to push the attached "nvptx: 'cuDeviceGetCount' failure is fatal"?

I think the real question is: what does a 'cuDeviceGetCount' fail mean?

Does it mean a serious error – or could it just be a permissions issue 
such that the user has no device access but otherwise is fine?

Because if it is, e.g., a permission problem – just returning '0' (no 
devices) would seem to be the proper solution.

But if it is expected to be always something serious, well, then a fatal 
error makes more sense.

The possible exit codes are:

CUDA_SUCCESS, CUDA_ERROR_DEINITIALIZED, CUDA_ERROR_NOT_INITIALIZED, 
CUDA_ERROR_INVALID_CONTEXT, CUDA_ERROR_INVALID_VALUE

which does not really help.

My impression is that 0 is usually returned if something goes wrong 
(e.g. with permissions) such that an error is a real exception. But all 
three choices seem to make about equally sense: either host fallback 
(with 0 or -1) or a fatal error.

Tobias