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Tensor Parallelism vs Pipeline Parallelism
Distributing 400B+ Parameter Models Across Multiple GPUs
When a model's weights exceed the memory of a single GPU (e.g. Llama 3.1 405B requires 810 GB in FP16), the harness must partition the model across multiple accelerators.
Parallelism Strategies
| Strategy | Partition Axis | Interconnect Requirement | Primary Bottleneck |
|---|---|---|---|
| Tensor Parallelism (TP) | Splits individual weight matrices within each layer | Ultra-high bandwidth (NVLink / NVSwitch @ 900 GB/s) | All-Reduce communication latency between tokens |
| Pipeline Parallelism (PP) | Splits sequential layers across different nodes/GPUs | Standard PCIe / InfiniBand network | Pipeline bubble idle time while waiting for downstream layers |
| Expert Parallelism (EP) | Distributes different MoE experts across different GPUs | InfiniBand / RoCE cluster network | All-to-All communication routing tokens to experts |
⌨ HANDS-ON LABConfigure 8-Way Tensor Parallel NVLink Topology
⭐ +250 XPShard a 405B parameter model across 8 GPUs using Tensor Parallelism with NVLink All-Reduce.
1Map model layers across 8 GPUs using Tensor Parallelism.
OBJECTIVE 1 / 1 — type "hint" if stuck
SYNAPSE VERIFICATION
QUERY 1 // 1
Why is Tensor Parallelism strictly limited to GPUs connected via NVLink within the same node?
Because PCIe cards cannot run CUDA
Because software licenses forbid multi-node TP
Because Ethernet cables do not support floating point numbers
Because TP requires All-Reduce communication on every single attention layer, demanding multi-hundred GB/s interconnect bandwidth to avoid stalling