memory-analysis

Memory Analysis for Ascend NPU

You are analyzing memory patterns for Ascend NPU optimization. This skill helps identify:

1. Data loading patterns and optimization opportunities
2. Host-device transfers (CPU ↔ NPU)
3. Automatic data migration effectiveness
4. Mixed precision opportunities (FP16/BF16)
5. Memory efficiency improvements

When to Use

Invoke this skill when:

• User asks about memory optimization for NPU
• Examining data loading and training pipelines
• Looking for memory inefficiencies
• Planning mixed precision training strategy

Analysis Approach

1. Data Loading Analysis

Examine:

• DataLoader configuration
• Batch size settings
• Number of workers
• Pin memory usage (.pin_memory=True)
• Prefetching strategies

Search Patterns:

grep -rn "DataLoader" <repo_path>
grep -rn "num_workers" <repo_path>
grep -rn "pin_memory" <repo_path>

2. Host-Device Transfer Patterns

Identify data movement:

# Explicit transfers
tensor = tensor.to('cuda')  # → .to('npu') or automatic
model = model.cuda()  # → .npu() or automatic

# Check for inefficient patterns
# - Redundant transfers
# - Transferring large unused data
# - Frequent CPU↔GPU bouncing

3. Automatic Data Migration

torch_npu provides automatic data migration:

• Tensors automatically move to NPU when needed
• Reduces explicit .to('npu') calls
• But may not cover all cases

Analyze:

• Will automatic migration work for this codebase?
• Are there cases preventing automatic migration?
• Performance impact of automatic vs explicit

4. Mixed Precision Training

FP16/BF16 Benefits on Ascend:

• 50% memory reduction
• 2-4x speedup on supported operations
• Better NPU utilization

Check for:

# Existing AMP usage
torch.cuda.amp.autocast  # → torch.npu.amp.autocast
torch.cuda.amp.GradScaler  # → torch.npu.amp.GradScaler

# Opportunities for AMP
# - Float32 models that can use FP16
# - Loss scaling requirements

5. Memory Efficiency Techniques

Identify opportunities:

• Gradient checkpointing: Trade compute for memory
• Gradient accumulation: Simulate larger batch sizes
• Memory pool reuse: NPU-specific memory optimization
• Tensor lifecycle: Proper cleanup to avoid leaks

Output Format

Data Loading Analysis

• DataLoader configuration summary
• Optimization opportunities:
  • Increase workers
  • Enable pin_memory (for NPU)
  • Adjust prefetch_factor
  • Use persistent_workers

Host-Device Transfer

• Current transfer patterns
• Redundant or inefficient transfers
• Automatic migration compatibility
• Recommendations:
  • Use automatic data migration where possible
  • Minimize explicit transfers
  • Keep frequently accessed data on NPU

Mixed Precision Opportunities

• Current precision usage (FP32/FP16)
• FP16/BF16 compatibility with torch.npu.amp
• Expected memory savings (up to 50%)
• Expected speedup (2-4x on supported ops)
• Implementation:

  # Enable torch_npu AMP
  from torch_npu import amp
  scaler = amp.GradScaler()
  with amp.autocast():
      output = model(input)
  

Memory Efficiency

• Gradient checkpointing opportunities
• Gradient accumulation for large effective batch sizes
• Memory pool optimization strategies
• Potential memory leaks or improper cleanup

Specific torch_npu APIs

Recommend specific APIs:

# Memory management
torch.npu.empty_cache()  # Clear unused memory
torch.npu.set_memory_strategy()  # Memory allocation strategy
torch.npu.memory_allocated()  # Current memory usage
torch.npu.max_memory_allocated()  # Peak memory

# AMP
from torch_npu import amp
amp.autocast()  # Automatic mixed precision
amp.GradScaler()  # Loss scaling

Tools to Use

Documentation First:

• Read official Ascend documentation before analysis:
  • https://www.hiascend.com/doc_center/source/zh/Pytorch/730/ptmoddevg/trainingmigrguide/PT_LMTMOG_0002.html

Memory Analysis:

• Use Grep to search for memory-related patterns
• Use Read to examine data loading code

Notes

• Ascend NPU has different memory hierarchy than GPU
• HBM (High Bandwidth Memory) is precious resource
• Automatic data migration reduces code changes
• Mixed precision training highly recommended for NPU
• Profile actual memory usage with npu-smi