Debugging inline PTX in Parallel Nsight

Question

Is it possible to view the PTX registers when stepping through inline PTX in Parallel Nsight?

I can set breakpoints on inline PTX and step through it, but hovering over the PTX registers does not show their values. I can turn on SASS and hovering on those registers does show their values, but it's hard to keep track of the relationships between the PTX registers and the SASS registers.

Answer 1

Unfortunately the GPU cannot execute PTX directly, it can only execute the SASS microcode. Because the JIT compiler in the driver (which translates PTX->SASS) does have the freedom to substantively change the PTX code during compilation, performing optimizations such as common subexpression elimination, your observations that 1) "it's hard to keep track of the relationships between the PTX registers and the SASS registers" and 2) you cannot examine PTX registers during execution are all too accurate.

I don't expect either of these limitations will be removed in the foreseeable future.