Running benchmarks locally

V8 performance is typically tracked using industry-standard benchmark suites that reflect real-world usage.

For modern V8 performance tracking, we recommend using:

• Speedometer: The current industry standard for measuring web application responsiveness.
• JetStream: Focuses on advanced web applications and includes JavaScript and WebAssembly.

CPU Configuration #

Before running benchmarks, ensure your CPU is configured for consistent results by setting the frequency scaling governor to performance.

sudo tools/cpu.sh fast

Internal Microbenchmarks #

V8 maintains a suite of microbenchmarks in test/js-perf-test for tracking the performance of specific language features. These are run using tools/run_perf.py:

tools/run_perf.py --arch x64 --binary-override-path out/x64.release/d8 test/js-perf-test/JSTests.json

For more details, see the testing guide.

Useful d8 Flags for Benchmarking #

Compiler Control #

• --no-opt: Disables all optimizing compilers (TurboFan, Maglev).
• --no-sparkplug: Disables the Sparkplug baseline compiler.
• --no-maglev: Disables the Maglev mid-tier compiler.
• --no-turbofan: Disables the TurboFan top-tier optimizing compiler.
• --trace-opt: Trace optimized compilation events.
• --trace-deopt: Trace deoptimization events.
• --trace-ic: Trace inline cache behavior.
• --print-opt-code: Print the generated machine code for optimized functions.
• --trace-turbo: Trace the TurboFan compilation pipeline (generates turbo-*.json and turbo-*.dot files).
• --trace-turbo-filter=<filter>: Only trace specific functions that match the filter.
• --trace-maglev: Same as --trace-turbo but for the Maglev compiler.

Profiling #

• --prof: Log statistical profiling information for CPU profiling. Use tools/linux-tick-processor (on Linux) to process the resulting v8.log.
• --log-timer-events: Log timer events (including console.time and internal V8 events).

Memory & Garbage Collection #

• --trace-gc: Print a trace line for each garbage collection.
• --max-semi-space-size=<MB>: Adjusts the young generation (nursery) heap size.
• --max-old-space-size=<MB>: Adjusts the old generation heap size.