Support FP8 NVLS multimem reduction

[Binyang2014]

Summary

• add FP16 accumulation support for FP8 NVLS multimem load-reduce
• probe and gate FP8 NVLS algorithms on device support
• keep MNNVL algorithm sizing and buffer-pool changes out of this sub-PR

Validation

• ./tools/lint.sh
• cmake --build build --target mscclpp_collectives mscclpp_nccl -j$(nproc)

[Copilot]

Pull request overview

This PR extends NVLS-based allreduce to better support FP8 by adding an FP16 accumulation path for multimem load+reduce, and by probing/gating FP8 NVLS algorithm selection based on device/runtime support (plumbed through the NCCL algorithm selector).

Changes:

• Add an FP8 NVLS support probe (isFp8NvlsSupported) and propagate an fp8NvlsSupported flag through the NCCL algorithm selector config.
• Add an optional FP16 accumulator variant for FP8 multimem load+reduce (via .acc::f16 instruction variants).
• Thread FP8 NVLS support gating into NVLS allreduce algorithm implementations.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/ext/nccl/nccl.cc	Computes FP8 NVLS support and passes it into the selector config.
src/ext/nccl/CMakeLists.txt	Adds collectives include path so NCCL extension can use collective utilities.
src/ext/nccl/algorithm_selector.hpp	Extends selector config with fp8NvlsSupported.
src/ext/nccl/algorithm_selector.cc	Gates NVLS selection for FP8 based on native FP8 and probed support.
src/ext/collectives/include/collective_utils.hpp	Declares FP8 dtype helpers and FP8 NVLS support probe API.
src/ext/collectives/include/allreduce/common.hpp	Extends multimem reduce helper to accept an accumulation type.
src/ext/collectives/include/allreduce/allreduce_nvls_zero_copy.hpp	Adds cached fp8NvlsSupported_ state to the algorithm class.
src/ext/collectives/include/allreduce/allreduce_nvls_warp_pipeline.hpp	Adds cached fp8NvlsSupported_ state to the algorithm class.
src/ext/collectives/include/allreduce/allreduce_nvls_block_pipeline.hpp	Adds cached fp8NvlsSupported_ state to the algorithm class.
src/ext/collectives/collective_utils.cu	Implements FP8 dtype checks and runtime FP8 NVLS support probing.
src/ext/collectives/allreduce/allreduce_nvls_zero_copy.cu	Adds AccumT plumbing for multimem load+reduce and runtime FP8 support gating.
src/ext/collectives/allreduce/allreduce_nvls_warp_pipeline.cu	Adds runtime FP8 NVLS support gating for this algorithm variant.
src/ext/collectives/allreduce/allreduce_nvls_block_pipeline.cu	Adds runtime FP8 NVLS support gating for this algorithm variant.
include/mscclpp/switch_channel_device.hpp	Adds FP16-accumulator multimem load+reduce variants for FP8 vector types.