[nsight-compute][source view] misaligned "live registers" with sources

Developer Tools Nsight Compute
1

Hello,

I am profiling a kernel with Nsight Compute. This kernel is heavily latency bound as it requires a lot of registers. I am trying to use the Live register count to optimize it.

However, some of the per-line register count don’t make sense to me. For instance, see the image attached where:

image
image2078×998 264 KB

On line 551 register count is 48, braces opens. In the braces, the register count increases which makes sense, brace closed on line 559. Then, on line 561 which is a comment, register count suddenly bumps to 112.

This does not makes sense to me, and I wonder if there is a misalignment of the live register with the source, due to the call to the inlined function “calcul_xg_tetra”. Could it be the case that there is a misalignment ?

Is there a specific thing to do to take these inline functions into account ?

Thanks in advance,
Rémi

I am compiling the code with nvc++ from Nvidia HPC SDK 25.3, with cuda 12.8 with drivers 570.133.07, on a Ubuntu 24.04 machine with a NVIDIA RTX 6000 Ada GPU. Moreover, the kernel is written using the Kokkos framework. My compilation flags include -lineinfo and my ncu run uses -import-sources. ncu version is 2025.1.0.0 (build 35237751) (public-release)

2

We fixed an issue related to correlation on the Source page when some but not all of the source files were resolved. Please try if there is a change to correlation when opening this report with Nsight Compute 2025.2.

3

Hi Felix, thanks for your answer.

I have downloaded ncu 2025.2, loaded up my ncu file, and the issue remains.

Should I generate the report with ncu 2025.2 too ?

Thanks,
Rémi

4

Should I generate the report with ncu 2025.2 too ?

I would not expect it to make a difference, no.

Further things you can try:

  • Share the report with us if that is acceptable to you, and we can have a look at it.
  • Inspect the SASS correlated with these high-level lines, to understand at which instructions the Live Registers metric changes/increases. You normally see spikes at CALL instructions, as the ABI requires the caller registers to be saved, which is included in the metric.
5

Hi !

What is the best way to send my report ? it is to large for the forum (60Mo)

Thanks