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Distributed Evaluation

Guide to running evaluation across multiple GPUs using data parallelism and tensor/pipeline parallelism.

Overview

Distributed evaluation speeds up benchmarking by:

Data Parallelism: Split evaluation samples across GPUs (each GPU has full model copy)
Tensor Parallelism: Split model weights across GPUs (for large models)
Pipeline Parallelism: Split model layers across GPUs (for very large models)

When to use:

Data Parallel: Model fits on single GPU, want faster evaluation
Tensor/Pipeline Parallel: Model too large for single GPU

HuggingFace Models (`hf`)

Data Parallelism (Recommended)

Each GPU loads a full copy of the model and processes a subset of evaluation data.

Single Node (8 GPUs):

accelerate launch --multi_gpu --num_processes 8 \
  -m lm_eval --model hf \
  --model_args pretrained=meta-llama/Llama-2-7b-hf,dtype=bfloat16 \
  --tasks mmlu,gsm8k,hellaswag \
  --batch_size 16

Speedup: Near-linear (8 GPUs = ~8× faster)

Memory: Each GPU needs full model (7B model ≈ 14GB × 8 = 112GB total)

Tensor Parallelism (Model Sharding)

Split model weights across GPUs for models too large for single GPU.

Without accelerate launcher:

lm_eval --model hf \
  --model_args \
    pretrained=meta-llama/Llama-2-70b-hf,\
    parallelize=True,\
    dtype=bfloat16 \
  --tasks mmlu,gsm8k \
  --batch_size 8

With 8 GPUs: 70B model (140GB) / 8 = 17.5GB per GPU ✅

Advanced sharding:

lm_eval --model hf \
  --model_args \
    pretrained=meta-llama/Llama-2-70b-hf,\
    parallelize=True,\
    device_map_option=auto,\
    max_memory_per_gpu=40GB,\
    max_cpu_memory=100GB,\
    dtype=bfloat16 \
  --tasks mmlu

Options:

device_map_option: "auto" (default), "balanced", "balanced_low_0"
max_memory_per_gpu: Max memory per GPU (e.g., "40GB")
max_cpu_memory: Max CPU memory for offloading
offload_folder: Disk offloading directory

Combined Data + Tensor Parallelism

Use both for very large models.

Example: 70B model on 16 GPUs (2 copies, 8 GPUs each):

accelerate launch --multi_gpu --num_processes 2 \
  -m lm_eval --model hf \
  --model_args \
    pretrained=meta-llama/Llama-2-70b-hf,\
    parallelize=True,\
    dtype=bfloat16 \
  --tasks mmlu \
  --batch_size 8

Result: 2× speedup from data parallelism, 70B model fits via tensor parallelism

Configuration with `accelerate config`

Create ~/.cache/huggingface/accelerate/default_config.yaml:

compute_environment: LOCAL_MACHINE
distributed_type: MULTI_GPU
num_machines: 1
num_processes: 8
gpu_ids: all
mixed_precision: bf16

Then run:

accelerate launch -m lm_eval --model hf \
  --model_args pretrained=meta-llama/Llama-2-7b-hf \
  --tasks mmlu

vLLM Models (`vllm`)

vLLM provides highly optimized distributed inference.

Tensor Parallelism

Single Node (4 GPUs):

lm_eval --model vllm \
  --model_args \
    pretrained=meta-llama/Llama-2-70b-hf,\
    tensor_parallel_size=4,\
    dtype=auto,\
    gpu_memory_utilization=0.9 \
  --tasks mmlu,gsm8k \
  --batch_size auto

Memory: 70B model split across 4 GPUs = ~35GB per GPU

Data Parallelism

Multiple model replicas:

lm_eval --model vllm \
  --model_args \
    pretrained=meta-llama/Llama-2-7b-hf,\
    data_parallel_size=4,\
    dtype=auto,\
    gpu_memory_utilization=0.8 \
  --tasks hellaswag,arc_challenge \
  --batch_size auto

Result: 4 model replicas = 4× throughput

Combined Tensor + Data Parallelism

Example: 8 GPUs = 4 TP × 2 DP:

lm_eval --model vllm \
  --model_args \
    pretrained=meta-llama/Llama-2-70b-hf,\
    tensor_parallel_size=4,\
    data_parallel_size=2,\
    dtype=auto,\
    gpu_memory_utilization=0.85 \
  --tasks mmlu \
  --batch_size auto

Result: 70B model fits (TP=4), 2× speedup (DP=2)

Multi-Node vLLM

vLLM doesn't natively support multi-node. Use Ray:

# Start Ray cluster
ray start --head --port=6379

# Run evaluation
lm_eval --model vllm \
  --model_args \
    pretrained=meta-llama/Llama-2-70b-hf,\
    tensor_parallel_size=8,\
    dtype=auto \
  --tasks mmlu

NVIDIA NeMo Models (`nemo_lm`)

Data Replication

8 replicas on 8 GPUs:

torchrun --nproc-per-node=8 --no-python \
  lm_eval --model nemo_lm \
  --model_args \
    path=/path/to/model.nemo,\
    devices=8 \
  --tasks hellaswag,arc_challenge \
  --batch_size 32

Speedup: Near-linear (8× faster)

Tensor Parallelism

4-way tensor parallelism:

torchrun --nproc-per-node=4 --no-python \
  lm_eval --model nemo_lm \
  --model_args \
    path=/path/to/70b_model.nemo,\
    devices=4,\
    tensor_model_parallel_size=4 \
  --tasks mmlu,gsm8k \
  --batch_size 16

Pipeline Parallelism

2 TP × 2 PP on 4 GPUs:

torchrun --nproc-per-node=4 --no-python \
  lm_eval --model nemo_lm \
  --model_args \
    path=/path/to/model.nemo,\
    devices=4,\
    tensor_model_parallel_size=2,\
    pipeline_model_parallel_size=2 \
  --tasks mmlu \
  --batch_size 8

Constraint: devices = TP × PP

Multi-Node NeMo

Currently not supported by lm-evaluation-harness.

SGLang Models (`sglang`)

Tensor Parallelism

lm_eval --model sglang \
  --model_args \
    pretrained=meta-llama/Llama-2-70b-hf,\
    tp_size=4,\
    dtype=auto \
  --tasks gsm8k \
  --batch_size auto

Data Parallelism (Deprecated)

Note: SGLang is deprecating data parallelism. Use tensor parallelism instead.

lm_eval --model sglang \
  --model_args \
    pretrained=meta-llama/Llama-2-7b-hf,\
    dp_size=4,\
    dtype=auto \
  --tasks mmlu

Performance Comparison

70B Model Evaluation (MMLU, 5-shot)

Method	GPUs	Time	Memory/GPU	Notes
HF (no parallel)	1	8 hours	140GB (OOM)	Won't fit
HF (TP=8)	8	2 hours	17.5GB	Slower, fits
HF (DP=8)	8	1 hour	140GB (OOM)	Won't fit
vLLM (TP=4)	4	30 min	35GB	Fast!
vLLM (TP=4, DP=2)	8	15 min	35GB	Fastest

7B Model Evaluation (Multiple Tasks)

Method	GPUs	Time	Speedup
HF (single)	1	4 hours	1×
HF (DP=4)	4	1 hour	4×
HF (DP=8)	8	30 min	8×
vLLM (DP=8)	8	15 min	16×

Takeaway: vLLM is significantly faster than HuggingFace for inference.

Choosing Parallelism Strategy

Decision Tree

Model fits on single GPU?
├─ YES: Use data parallelism
│   ├─ HF: accelerate launch --multi_gpu --num_processes N
│   └─ vLLM: data_parallel_size=N (fastest)
│
└─ NO: Use tensor/pipeline parallelism
    ├─ Model < 70B:
    │   └─ vLLM: tensor_parallel_size=4
    ├─ Model 70-175B:
    │   ├─ vLLM: tensor_parallel_size=8
    │   └─ Or HF: parallelize=True
    └─ Model > 175B:
        └─ Contact framework authors

Memory Estimation

Rule of thumb:

Memory (GB) = Parameters (B) × Precision (bytes) × 1.2 (overhead)

Examples:

7B FP16: 7 × 2 × 1.2 = 16.8GB ✅ Fits A100 40GB
13B FP16: 13 × 2 × 1.2 = 31.2GB ✅ Fits A100 40GB
70B FP16: 70 × 2 × 1.2 = 168GB ❌ Need TP=4 or TP=8
70B BF16: 70 × 2 × 1.2 = 168GB (same as FP16)

With tensor parallelism:

Memory per GPU = Total Memory / TP

70B on 4 GPUs: 168GB / 4 = 42GB per GPU ✅
70B on 8 GPUs: 168GB / 8 = 21GB per GPU ✅

Multi-Node Evaluation

HuggingFace with SLURM

Submit job:

#!/bin/bash
#SBATCH --nodes=4
#SBATCH --gpus-per-node=8
#SBATCH --ntasks-per-node=1

srun accelerate launch --multi_gpu \
  --num_processes $((SLURM_NNODES * 8)) \
  -m lm_eval --model hf \
  --model_args pretrained=meta-llama/Llama-2-7b-hf \
  --tasks mmlu,gsm8k,hellaswag \
  --batch_size 16

Submit:

sbatch eval_job.sh

Manual Multi-Node Setup

On each node, run:

accelerate launch \
  --multi_gpu \
  --num_machines 4 \
  --num_processes 32 \
  --main_process_ip $MASTER_IP \
  --main_process_port 29500 \
  --machine_rank $NODE_RANK \
  -m lm_eval --model hf \
  --model_args pretrained=meta-llama/Llama-2-7b-hf \
  --tasks mmlu

Environment variables:

MASTER_IP: IP of rank 0 node
NODE_RANK: 0, 1, 2, 3 for each node

Best Practices

1. Start Small

Test on small sample first:

lm_eval --model hf \
  --model_args pretrained=meta-llama/Llama-2-70b-hf,parallelize=True \
  --tasks mmlu \
  --limit 100  # Just 100 samples

2. Monitor GPU Usage

# Terminal 1: Run evaluation
lm_eval --model hf ...

# Terminal 2: Monitor
watch -n 1 nvidia-smi

Look for:

GPU utilization > 90%
Memory usage stable
All GPUs active

3. Optimize Batch Size

# Auto batch size (recommended)
--batch_size auto

# Or tune manually
--batch_size 16  # Start here
--batch_size 32  # Increase if memory allows

4. Use Mixed Precision

--model_args dtype=bfloat16  # Faster, less memory

5. Check Communication

For data parallelism, check network bandwidth:

# Should see InfiniBand or high-speed network
nvidia-smi topo -m

Troubleshooting

"CUDA out of memory"

Solutions:

Increase tensor parallelism:

--model_args tensor_parallel_size=8  # Was 4

Reduce batch size:
```
--batch_size 4  # Was 16
```

Lower precision:

--model_args dtype=int8  # Quantization

"NCCL error" or Hanging

Check:

All GPUs visible: nvidia-smi
NCCL installed: python -c "import torch; print(torch.cuda.nccl.version())"
Network connectivity between nodes

Fix:

export NCCL_DEBUG=INFO  # Enable debug logging
export NCCL_IB_DISABLE=0  # Use InfiniBand if available

Slow Evaluation

Possible causes:

Data loading bottleneck: Preprocess dataset
Low GPU utilization: Increase batch size
Communication overhead: Reduce parallelism degree

Profile:

lm_eval --model hf \
  --model_args pretrained=meta-llama/Llama-2-7b-hf \
  --tasks mmlu \
  --limit 100 \
  --log_samples  # Check timing

GPUs Imbalanced

Symptom: GPU 0 at 100%, others at 50%

Solution: Use device_map_option=balanced:

--model_args parallelize=True,device_map_option=balanced

Example Configurations

Small Model (7B) - Fast Evaluation

# 8 A100s, data parallel
accelerate launch --multi_gpu --num_processes 8 \
  -m lm_eval --model hf \
  --model_args \
    pretrained=meta-llama/Llama-2-7b-hf,\
    dtype=bfloat16 \
  --tasks mmlu,gsm8k,hellaswag,arc_challenge \
  --num_fewshot 5 \
  --batch_size 32

# Time: ~30 minutes

Large Model (70B) - vLLM

# 8 H100s, tensor parallel
lm_eval --model vllm \
  --model_args \
    pretrained=meta-llama/Llama-2-70b-hf,\
    tensor_parallel_size=8,\
    dtype=auto,\
    gpu_memory_utilization=0.9 \
  --tasks mmlu,gsm8k,humaneval \
  --num_fewshot 5 \
  --batch_size auto

# Time: ~1 hour

Very Large Model (175B+)

Requires specialized setup - contact framework maintainers

References

HuggingFace Accelerate: https://huggingface.co/docs/accelerate/
vLLM docs: https://docs.vllm.ai/
NeMo docs: https://docs.nvidia.com/nemo-framework/
lm-eval distributed guide: docs/model_guide.md

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Distributed Evaluation

Overview

HuggingFace Models (hf)

Data Parallelism (Recommended)

Tensor Parallelism (Model Sharding)

Combined Data + Tensor Parallelism

Configuration with accelerate config

vLLM Models (vllm)

Tensor Parallelism

Data Parallelism

Combined Tensor + Data Parallelism

Multi-Node vLLM

NVIDIA NeMo Models (nemo_lm)

Data Replication

Tensor Parallelism

Pipeline Parallelism

Multi-Node NeMo

SGLang Models (sglang)

Tensor Parallelism

Data Parallelism (Deprecated)

Performance Comparison

70B Model Evaluation (MMLU, 5-shot)

7B Model Evaluation (Multiple Tasks)

Choosing Parallelism Strategy

Decision Tree

Memory Estimation

Multi-Node Evaluation

HuggingFace with SLURM

Manual Multi-Node Setup

Best Practices

1. Start Small

2. Monitor GPU Usage

3. Optimize Batch Size

4. Use Mixed Precision

5. Check Communication

Troubleshooting

"CUDA out of memory"

"NCCL error" or Hanging

Slow Evaluation

GPUs Imbalanced

Example Configurations

Small Model (7B) - Fast Evaluation

Large Model (70B) - vLLM

Very Large Model (175B+)

References

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HuggingFace Models (`hf`)

Configuration with `accelerate config`

vLLM Models (`vllm`)

NVIDIA NeMo Models (`nemo_lm`)

SGLang Models (`sglang`)