Linex: Source-Level GPU Performance Profiling

Map GPU performance metrics to your source code lines. Get cycle-level timing, stall analysis, and instruction-level metrics for each line of source code.

When to Use

• User asks to profile a GPU application at source-line granularity
• Need to identify which specific lines of code are performance bottlenecks
• Analyzing stall patterns and execution bottlenecks at the source level
• Understanding cycle-level timing for each line of code
• Instruction-level analysis mapped to source lines

Instructions

1. Ensure the target runs on AMD ROCm 7.0+ with rocprofv3 available.
2. Kernels must be compiled with -g (debug symbols) for source mapping.
3. Choose execution path:
   • If a Linex MCP server is available, use its MCP tools:
     • profile_application to run and profile a target application with the options below.
     • analyze_instruction_hotspots to perform instruction-level hotspot analysis on collected profiles.
   • Otherwise use the Python API from the environment where Linex is installed.

Python API

from linex import Linex

profiler = Linex(
    target_cu=0,                      # Target compute unit
    shader_engine_mask="0xFFFFFFFF",  # All shader engines
    activity=10,                      # Activity counter polling
)

profiler.profile("./my_app", kernel_filter="my_kernel")

# Show hotspots (sorted by total_cycles)
for line in profiler.source_lines[:5]:
    print(f"{line.file}:{line.line_number}")
    print(f"  {line.total_cycles:,} cycles ({line.stall_percent:.1f}% stalled)")
    print(f"  Executed {line.execution_count} times")

# Find memory-bound lines
memory_bound = [
    l for l in profiler.source_lines 
    if l.stall_percent > 50
]

# Instruction-level analysis
for line in profiler.source_lines[:1]:
    for inst in line.instructions:
        print(f"{inst.isa}: {inst.latency_cycles} cycles")

SourceLine Properties

• file - Source file path
• line_number - Line number
• total_cycles - Sum of all instruction cycles
• stall_cycles - Cycles spent waiting
• idle_cycles - Cycles slot was idle
• execution_count - Total executions
• instructions - List of ISA instructions
• stall_percent - Convenience: stall_cycles / total_cycles * 100

InstructionData Properties

• isa - ISA instruction text
• latency_cycles - Total cycles for this instruction
• stall_cycles - Cycles spent waiting
• idle_cycles - Cycles slot was idle
• execution_count - How many times it ran
• instruction_address - Virtual address in GPU memory
• file - Parsed from source_location
• line - Parsed from source_location
• stall_percent - Convenience: stall_cycles / latency_cycles * 100

Workflow

1. Ensure the target binary is built with -g (debug symbols) for source mapping.
2. Create a Linex() profiler; optionally set target_cu, shader_engine_mask, or activity.
3. Call profiler.profile(command, kernel_filter=...) to run profiling.
4. Access profiler.source_lines (sorted by total_cycles) to find hotspots.
5. Use line.stall_percent to identify memory-bound or dependency-bound lines.
6. Drill down into line.instructions for instruction-level analysis.
7. Use relative paths for the target binary so the skill is portable.

Notes

• Requires ROCm 7.0+ with rocprofv3 support.
• Source mapping requires kernels compiled with -g (debug symbols).
• source_lines are automatically sorted by total_cycles (descending).
• Use kernel_filter to profile specific kernels by name (regex pattern).
• For Triton or other frameworks, ensure debug symbols are available in the compiled output.