[Bug]: Compilation error in uballocator when ENABLE_MULTI_DEVICE=0

[WilliamTambellini]

System Info

TRTLLM today's main branch.
cmake 3.27.
gcc 11
RHEL8
CUDA 12.9

Who can help?

@tongyuantongyu

Information

• The official example scripts
• My own modified scripts

Tasks

• An officially supported task in the examples folder (such as GLUE/SQuAD, ...)
• My own task or dataset (give details below)

Reproduction

Try to build without ENABLE_MULTI_DEVICE:

cmake ..  -DCMAKE_VERBOSE_MAKEFILE=ON  -DBUILD_PYBIND=OFF   -DENABLE_MULTI_DEVICE=OFF

See cmake runs correctly.
But compiling fails afterward.

Expected behavior

compilation success.

actual behavior

See compilation error when trying to build the userbuffer kernel:

In file included from TensorRT-LLM/cpp/tensorrt_llm/kernels/userbuffers/ub_interface.h:20,
                 from TensorRT-LLM/cpp/tensorrt_llm/kernels/userbuffers/ub_interface.cpp:16:
TensorRT-LLM/cpp/tensorrt_llm/kernels/userbuffers/ub_allocator.h:38:5: 
error: ‘ncclWindow_t’ does not name a type
   38 |     ncclWindow_t window;

additional notes

It s because when ENABLE_MULTI_DEVICE=OFF, the cmake script does not search for nccl so no src code should try to include/use nccl structs.

Possible solutions:
1 move the UBBuffer inside the ENABLE_MULTI_DEVICE block:

#if ENABLE_MULTI_DEVICE
struct UBBuffer
{
    void* addr;
    int handle;
    size_t size;
    ncclWindow_t window;

2 Keep the UBBuffer class but ifdef the "ncclWindow_t window;" line

struct UBBuffer
{
    void* addr;
    int handle;
    size_t size;
#if ENABLE_MULTI_DEVICE
    ncclWindow_t window;
#endif

I can prepare a PR if you d advice which solution you d prefer.
Best

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[Puranjay-del-Mishra]

Hey @WilliamTambellini
I would like to contribute here if you haven't made a PR for this already!

[WilliamTambellini]

Tks @Puranjay-del-Mishra but that one is a blocker so I would prefer to do it myself, plus I ve already done some PRs in this repo so I know what to expect.

[karljang]

@WilliamTambellini, I think solution.1 needs more work to solve other compile errors, while solution.2 may work but should be reviewed. Would you be able to raise a PR first so we can ask reviews from others?

[WilliamTambellini]

Yes I m going to push a draft PullRequest.
Short term I ve simply

#if ENABLE_MULTI_DEVICE
  #include "nccl.h"
  #include "userbuffers.h"
  #ifdef _WIN32
   #include <windows.h>
  #else
   #include <dlfcn.h>
 #endif
#else
  using ncclWindow_t = void*;
#endif

but we ll likely need to also throw if one tries to create/use a cross device UBBuffer in single device build... TBC.

[WilliamTambellini]

#6874