dtvm-perf-profile

name

dtvm-perf-profile

description

Profile DTVM execution using Linux perf and generate categorized analysis reports. Use when the user wants to profile a DTVM command, find performance hotspots, break down JIT-compiled EVM basic block execution time, analyze host function overhead, or mentions "perf", "profile", "hotspot", "breakdown", or "bottleneck" in the context of DTVM execution. The user provides a dtvm command line (including bytecode path, calldata, execution mode, etc.).

DTVM Perf Profiling

Profile DTVM execution and produce a categorized performance report.

Prerequisites

1. perf binary: Either system perf or a self-built one (check repo root for ./perf).
2. Build with ZEN_ENABLE_LINUX_PERF=ON: Required for per-basic-block JIT symbols.

cmake -B build -DCMAKE_BUILD_TYPE=Release \
  -DZEN_ENABLE_MULTIPASS_JIT=ON \
  -DZEN_ENABLE_LINUX_PERF=ON \
  -DLLVM_DIR=/opt/llvm15/lib/cmake/llvm
cmake --build build -j$(nproc)

For singlepass JIT, replace -DZEN_ENABLE_MULTIPASS_JIT=ON with -DZEN_ENABLE_SINGLEPASS_JIT=ON (no LLVM needed).

Workflow

1. Verify build flags

Check CMakeCache.txt for ZEN_ENABLE_LINUX_PERF:BOOL=ON. If OFF, reconfigure and rebuild.

2. Run the profiling script

.agents/skills/dtvm-perf-profile/scripts/perf_profile.sh \
  --perf ./perf --output-dir perf_results -- \
  ./build/dtvm -m multipass --format evm --gas-limit 0xFFFFFFFFFFFF \
  <bytecode.hex> \
  --calldata <hex> \
  --load-state <state.json> \
  --contract-address <addr> \
  --num-extra-compilations=0 --num-extra-executions=99999

The script lives under the skill SSOT at <repo>/.agents/skills/dtvm-perf-profile/scripts/perf_profile.sh — not under the .claude/skills/ mirror.

Key flags for the dtvm command:

• --num-extra-executions=N: More iterations = better sampling of execution (vs compilation). Use 99999+ for meaningful data.
• --enable-statistics: Optional. Adds timer-based breakdown but introduces ~10% overhead from clock_gettime. Omit for cleaner perf samples.
• --num-extra-compilations=0: Avoid repeated compilations unless profiling compilation itself.

3. Interpret the summary

The script generates perf_summary.txt with these categories:

Category	What it measures
EVM Basic Block Hotspots	Time in JIT-compiled EVM code, per BB (e.g. EVMBB0_JUMPDEST_1405)
EVM Host Functions	Time in host calls (evmEmitLog3, evmGetSLoad, etc.)
Keccak / Hashing	Time in keccakf1600_bmi / ethash_keccak256
JIT Compilation	Register allocator, ISel, MC lowering (only for first compilation)
Profiling Overhead	clock_gettime overhead from --enable-statistics
Memory Allocation	malloc/free from instantiation and host calls
Instantiation	EVMInstance creation/destruction per execution
By DSO	High-level split: dtvm binary vs libc vs jitted SOs vs vdso

4. Drill into hotspots

For any hot symbol, annotate its assembly:

./perf annotate -i perf_results/perf_dtvm_jit.data -s EVMBB0_JUMPDEST_1405

5. Present findings

Structure the report as:

1. Setup: Command, build flags, iteration count
2. Top-level split: Compilation vs Execution vs Instantiation (from --enable-statistics if used, or from DSO breakdown)
3. Execution breakdown: Table of BB hotspots + host functions + keccak, sorted by overhead
4. Observations: Notable findings (e.g. profiling overhead, dominant BBs, hash cost)
5. Recommendations: Actionable next steps

BB Symbol Naming

EVM basic block symbols follow the pattern EVMBB<funcIdx>_<type>_<evmPC>:

• EVMBB0_MAIN_ENTRY_1 -- contract entry point
• EVMBB0_JUMPDEST_<pc> -- basic block at EVM PC (JUMPDEST opcode)
• EVMBB0_SWITCH<n>_<pc> -- jump dispatch table

The EVM PC can be cross-referenced with the contract's disassembly to identify which Solidity function or logic the BB belongs to.

Tips

• Reduce noise: Omit --enable-statistics for cleaner perf data (avoids ~10% clock_gettime overhead).
• Increase signal: Use high --num-extra-executions (100K+) so execution dominates over one-time compilation.
• Compare modes: Profile same contract with -m singlepass vs -m multipass to compare JIT backends.
• Interpreter baseline: Profile with -m interpreter (no ZEN_ENABLE_LINUX_PERF needed) for comparison.