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Question

I've built some C++ code that uses OpenACC and compiled it with the PGI compiler for use on the Tesla GPU.

Compilation succeeds without any warnings.

I run the program and get two errors:

call to cuStreamSynchronize returned error 717: Invalid address space
call to cuMemFreeHost returned error 717: Invalid address space

The internet doesn't seem to know much about this, other than to suggest enabling unified memory so that the problem is automatically swept under the rug. I'm not into that kind of solution.

How do I go about debugging this?

With C++ code running only on the CPU, I'd fire up gdb, do a backtrace, and say, "Ah ha!"

But now I have code living on the CPU and the GPU and data flowing between the two. I don't even know what tools to use.

A fallback is to start commenting out lines until the problem goes away, but that seems suboptimal too.

Answer

There are some helpful environment variables that aid in debugging. Any combination can be enabled:

export PGI_ACC_TIME=1   #Profile time usage
export PGI_ACC_NOTIFY=1 #Set to values 0-3 where 3 is the most detailed
export PGI_ACC_DEBUG=1  #Extra debugging info