You are viewing documentation generated from a user contribution or an upcoming release. The contents of this document may not have been reviewed by the Deno team. Click here to view the documentation for the latest release.
Edit

Profiling

Perf profiling:

Tools that can be used to generate/ visualise perf results:

Example using perf on micro_bench_ops and visualising using flamescope:

# build `examples/micro_bench_ops`
cargo build --release --example micro_bench_ops

# run `examples/micro_bench_ops` using perf
sudo perf record -F 49 -a -g -- ./target/release/examples/micro_bench_ops
sudo perf script --header > micro_bench_ops_perf

# now open the file using flamescope

Example running deno_tcp.ts in combination with flamegraph (script.sh):

sudo flamegraph -o flamegraph.svg target/debug/deno run --allow-net cli/bench/deno_tcp.ts &
sleep 1
./third_party/prebuilt/linux64/wrk http://localhost:4500/
sleep 1
kill `pgrep perf`

v8 profiling:

Example using v8 profiling on micro_bench_ops:

# build `examples/micro_bench_ops`
cargo build --release --example micro_bench_ops

# run `examples/micro_bench_ops`
./target/release/examples/micro_bench_ops --prof

Example using v8 profiling on deno_tcp.ts:

# build `deno`
cargo build --release

# run `deno_tcp.ts`
./target/release/deno --v8-flags=--prof --allow-net cli/bench/deno_tcp.ts &
sleep 1
./third_party/prebuilt/linux64/wrk http://localhost:4500/
sleep 1
kill `pgrep deno`

V8 will write a file in the current directory that looks like this: isolate-0x7fad98242400-v8.log. To examine this file:

node --prof-process isolate-0x7fad98242400-v8.log > prof.log

prof.log will contain information about tick distribution of different calls.

To view the log with Web UI, generate JSON file of the log:

Open rusty_v8/v8/tools/profview/index.html in your browser, and select prof.json to view the distribution graphically.

Useful V8 flags during profiling:

  • --prof
  • --log-internal-timer-events
  • --log-timer-events
  • --track-gc
  • --log-source-code
  • --track-gc-object-stats

To learn more about profiling, check out the following links:

Debugging with LLDB

To debug the deno binary, we can use rust-lldb. It should come with rustc and is a wrapper around LLDB.

$ rust-lldb -- ./target/debug/deno run --allow-net tests/http_bench.ts
# On macOS, you might get warnings like
# `ImportError: cannot import name _remove_dead_weakref`
# In that case, use system python by setting PATH, e.g.
# PATH=/System/Library/Frameworks/Python.framework/Versions/2.7/bin:$PATH
(lldb) command script import "/Users/kevinqian/.rustup/toolchains/1.36.0-x86_64-apple-darwin/lib/rustlib/etc/lldb_rust_formatters.py"
(lldb) type summary add --no-value --python-function lldb_rust_formatters.print_val -x ".*" --category Rust
(lldb) type category enable Rust
(lldb) target create "../deno/target/debug/deno"
Current executable set to '../deno/target/debug/deno' (x86_64).
(lldb) settings set -- target.run-args  "tests/http_bench.ts" "--allow-net"
(lldb) b op_start
(lldb) r

V8 flags

V8 has many many internal command-line flags:

$ deno run --v8-flags=--help _
SSE3=1 SSSE3=1 SSE4_1=1 SSE4_2=1 SAHF=1 AVX=1 FMA3=1 BMI1=1 BMI2=1 LZCNT=1 POPCNT=1 ATOM=0
Synopsis:
  shell [options] [--shell] [<file>...]
  d8 [options] [-e <string>] [--shell] [[--module] <file>...]

  -e        execute a string in V8
  --shell   run an interactive JavaScript shell
  --module  execute a file as a JavaScript module

Note: the --module option is implicitly enabled for *.mjs files.

The following syntax for options is accepted (both '-' and '--' are ok):
  --flag        (bool flags only)
  --no-flag     (bool flags only)
  --flag=value  (non-bool flags only, no spaces around '=')
  --flag value  (non-bool flags only)
  --            (captures all remaining args in JavaScript)

Options:
  --use-strict (enforce strict mode)
        type: bool  default: false
  --es-staging (enable test-worthy harmony features (for internal use only))
        type: bool  default: false
  --harmony (enable all completed harmony features)
        type: bool  default: false
  --harmony-shipping (enable all shipped harmony features)
        type: bool  default: true
  --harmony-regexp-sequence (enable "RegExp Unicode sequence properties" (in progress))
        type: bool  default: false
  --harmony-weak-refs-with-cleanup-some (enable "harmony weak references with FinalizationRegistry.prototype.cleanupSome" (in progress))
        type: bool  default: false
  --harmony-regexp-match-indices (enable "harmony regexp match indices" (in progress))
        type: bool  default: false
  --harmony-top-level-await (enable "harmony top level await")
        type: bool  default: false
  --harmony-namespace-exports (enable "harmony namespace exports (export * as foo from 'bar')")
        type: bool  default: true
  --harmony-sharedarraybuffer (enable "harmony sharedarraybuffer")
        type: bool  default: true
  --harmony-import-meta (enable "harmony import.meta property")
        type: bool  default: true
  --harmony-dynamic-import (enable "harmony dynamic import")
        type: bool  default: true
  --harmony-promise-all-settled (enable "harmony Promise.allSettled")
        type: bool  default: true
  --harmony-promise-any (enable "harmony Promise.any")
        type: bool  default: true
  --harmony-private-methods (enable "harmony private methods in class literals")
        type: bool  default: true
  --harmony-weak-refs (enable "harmony weak references")
        type: bool  default: true
  --harmony-string-replaceall (enable "harmony String.prototype.replaceAll")
        type: bool  default: true
  --harmony-logical-assignment (enable "harmony logical assignment")
        type: bool  default: true
  --lite-mode (enables trade-off of performance for memory savings)
        type: bool  default: false
  --future (Implies all staged features that we want to ship in the not-too-far future)
        type: bool  default: false
  --assert-types (generate runtime type assertions to test the typer)
        type: bool  default: false
  --allocation-site-pretenuring (pretenure with allocation sites)
        type: bool  default: true
  --page-promotion (promote pages based on utilization)
        type: bool  default: true
  --always-promote-young-mc (always promote young objects during mark-compact)
        type: bool  default: true
  --page-promotion-threshold (min percentage of live bytes on a page to enable fast evacuation)
        type: int  default: 70
  --trace-pretenuring (trace pretenuring decisions of HAllocate instructions)
        type: bool  default: false
  --trace-pretenuring-statistics (trace allocation site pretenuring statistics)
        type: bool  default: false
  --track-fields (track fields with only smi values)
        type: bool  default: true
  --track-double-fields (track fields with double values)
        type: bool  default: true
  --track-heap-object-fields (track fields with heap values)
        type: bool  default: true
  --track-computed-fields (track computed boilerplate fields)
        type: bool  default: true
  --track-field-types (track field types)
        type: bool  default: true
  --trace-block-coverage (trace collected block coverage information)
        type: bool  default: false
  --trace-protector-invalidation (trace protector cell invalidations)
        type: bool  default: false
  --feedback-normalization (feed back normalization to constructors)
        type: bool  default: false
  --enable-one-shot-optimization (Enable size optimizations for the code that will only be executed once)
        type: bool  default: false
  --unbox-double-arrays (automatically unbox arrays of doubles)
        type: bool  default: true
  --interrupt-budget (interrupt budget which should be used for the profiler counter)
        type: int  default: 147456
  --jitless (Disable runtime allocation of executable memory.)
        type: bool  default: false
  --use-ic (use inline caching)
        type: bool  default: true
  --budget-for-feedback-vector-allocation (The budget in amount of bytecode executed by a function before we decide to allocate feedback vectors)
        type: int  default: 1024
  --lazy-feedback-allocation (Allocate feedback vectors lazily)
        type: bool  default: true
  --ignition-elide-noneffectful-bytecodes (elide bytecodes which won't have any external effect)
        type: bool  default: true
  --ignition-reo (use ignition register equivalence optimizer)
        type: bool  default: true
  --ignition-filter-expression-positions (filter expression positions before the bytecode pipeline)
        type: bool  default: true
  --ignition-share-named-property-feedback (share feedback slots when loading the same named property from the same object)
        type: bool  default: true
  --print-bytecode (print bytecode generated by ignition interpreter)
        type: bool  default: false
  --enable-lazy-source-positions (skip generating source positions during initial compile but regenerate when actually required)
        type: bool  default: true
  --stress-lazy-source-positions (collect lazy source positions immediately after lazy compile)
        type: bool  default: false
  --print-bytecode-filter (filter for selecting which functions to print bytecode)
        type: string  default: *
  --trace-ignition-codegen (trace the codegen of ignition interpreter bytecode handlers)
        type: bool  default: false
  --trace-ignition-dispatches (traces the dispatches to bytecode handlers by the ignition interpreter)
        type: bool  default: false
  --trace-ignition-dispatches-output-file (the file to which the bytecode handler dispatch table is written (by default, the table is not written to a file))
        type: string  default: nullptr
  --fast-math (faster (but maybe less accurate) math functions)
        type: bool  default: true
  --trace-track-allocation-sites (trace the tracking of allocation sites)
        type: bool  default: false
  --trace-migration (trace object migration)
        type: bool  default: false
  --trace-generalization (trace map generalization)
        type: bool  default: false
  --turboprop (enable experimental turboprop mid-tier compiler.)
        type: bool  default: false
  --concurrent-recompilation (optimizing hot functions asynchronously on a separate thread)
        type: bool  default: true
  --trace-concurrent-recompilation (track concurrent recompilation)
        type: bool  default: false
  --concurrent-recompilation-queue-length (the length of the concurrent compilation queue)
        type: int  default: 8
  --concurrent-recompilation-delay (artificial compilation delay in ms)
        type: int  default: 0
  --block-concurrent-recompilation (block queued jobs until released)
        type: bool  default: false
  --concurrent-inlining (run optimizing compiler's inlining phase on a separate thread)
        type: bool  default: false
  --max-serializer-nesting (maximum levels for nesting child serializers)
        type: int  default: 25
  --trace-heap-broker-verbose (trace the heap broker verbosely (all reports))
        type: bool  default: false
  --trace-heap-broker-memory (trace the heap broker memory (refs analysis and zone numbers))
        type: bool  default: false
  --trace-heap-broker (trace the heap broker (reports on missing data only))
        type: bool  default: false
  --stress-runs (number of stress runs)
        type: int  default: 0
  --deopt-every-n-times (deoptimize every n times a deopt point is passed)
        type: int  default: 0
  --print-deopt-stress (print number of possible deopt points)
        type: bool  default: false
  --opt (use adaptive optimizations)
        type: bool  default: true
  --turbo-sp-frame-access (use stack pointer-relative access to frame wherever possible)
        type: bool  default: false
  --turbo-control-flow-aware-allocation (consider control flow while allocating registers)
        type: bool  default: true
  --turbo-filter (optimization filter for TurboFan compiler)
        type: string  default: *
  --trace-turbo (trace generated TurboFan IR)
        type: bool  default: false
  --trace-turbo-path (directory to dump generated TurboFan IR to)
        type: string  default: nullptr
  --trace-turbo-filter (filter for tracing turbofan compilation)
        type: string  default: *
  --trace-turbo-graph (trace generated TurboFan graphs)
        type: bool  default: false
  --trace-turbo-scheduled (trace TurboFan IR with schedule)
        type: bool  default: false
  --trace-turbo-cfg-file (trace turbo cfg graph (for C1 visualizer) to a given file name)
        type: string  default: nullptr
  --trace-turbo-types (trace TurboFan's types)
        type: bool  default: true
  --trace-turbo-scheduler (trace TurboFan's scheduler)
        type: bool  default: false
  --trace-turbo-reduction (trace TurboFan's various reducers)
        type: bool  default: false
  --trace-turbo-trimming (trace TurboFan's graph trimmer)
        type: bool  default: false
  --trace-turbo-jt (trace TurboFan's jump threading)
        type: bool  default: false
  --trace-turbo-ceq (trace TurboFan's control equivalence)
        type: bool  default: false
  --trace-turbo-loop (trace TurboFan's loop optimizations)
        type: bool  default: false
  --trace-turbo-alloc (trace TurboFan's register allocator)
        type: bool  default: false
  --trace-all-uses (trace all use positions)
        type: bool  default: false
  --trace-representation (trace representation types)
        type: bool  default: false
  --turbo-verify (verify TurboFan graphs at each phase)
        type: bool  default: false
  --turbo-verify-machine-graph (verify TurboFan machine graph before instruction selection)
        type: string  default: nullptr
  --trace-verify-csa (trace code stubs verification)
        type: bool  default: false
  --csa-trap-on-node (trigger break point when a node with given id is created in given stub. The format is: StubName,NodeId)
        type: string  default: nullptr
  --turbo-stats (print TurboFan statistics)
        type: bool  default: false
  --turbo-stats-nvp (print TurboFan statistics in machine-readable format)
        type: bool  default: false
  --turbo-stats-wasm (print TurboFan statistics of wasm compilations)
        type: bool  default: false
  --turbo-splitting (split nodes during scheduling in TurboFan)
        type: bool  default: true
  --function-context-specialization (enable function context specialization in TurboFan)
        type: bool  default: false
  --turbo-inlining (enable inlining in TurboFan)
        type: bool  default: true
  --max-inlined-bytecode-size (maximum size of bytecode for a single inlining)
        type: int  default: 500
  --max-inlined-bytecode-size-cumulative (maximum cumulative size of bytecode considered for inlining)
        type: int  default: 1000
  --max-inlined-bytecode-size-absolute (maximum cumulative size of bytecode considered for inlining)
        type: int  default: 5000
  --reserve-inline-budget-scale-factor (maximum cumulative size of bytecode considered for inlining)
        type: float  default: 1.2
  --max-inlined-bytecode-size-small (maximum size of bytecode considered for small function inlining)
        type: int  default: 30
  --max-optimized-bytecode-size (maximum bytecode size to be considered for optimization; too high values may cause the compiler to hit (release) assertions)
        type: int  default: 61440
  --min-inlining-frequency (minimum frequency for inlining)
        type: float  default: 0.15
  --polymorphic-inlining (polymorphic inlining)
        type: bool  default: true
  --stress-inline (set high thresholds for inlining to inline as much as possible)
        type: bool  default: false
  --trace-turbo-inlining (trace TurboFan inlining)
        type: bool  default: false
  --turbo-inline-array-builtins (inline array builtins in TurboFan code)
        type: bool  default: true
  --use-osr (use on-stack replacement)
        type: bool  default: true
  --trace-osr (trace on-stack replacement)
        type: bool  default: false
  --analyze-environment-liveness (analyze liveness of environment slots and zap dead values)
        type: bool  default: true
  --trace-environment-liveness (trace liveness of local variable slots)
        type: bool  default: false
  --turbo-load-elimination (enable load elimination in TurboFan)
        type: bool  default: true
  --trace-turbo-load-elimination (trace TurboFan load elimination)
        type: bool  default: false
  --turbo-profiling (enable basic block profiling in TurboFan)
        type: bool  default: false
  --turbo-profiling-verbose (enable basic block profiling in TurboFan, and include each function's schedule and disassembly in the output)
        type: bool  default: false
  --turbo-verify-allocation (verify register allocation in TurboFan)
        type: bool  default: false
  --turbo-move-optimization (optimize gap moves in TurboFan)
        type: bool  default: true
  --turbo-jt (enable jump threading in TurboFan)
        type: bool  default: true
  --turbo-loop-peeling (Turbofan loop peeling)
        type: bool  default: true
  --turbo-loop-variable (Turbofan loop variable optimization)
        type: bool  default: true
  --turbo-loop-rotation (Turbofan loop rotation)
        type: bool  default: true
  --turbo-cf-optimization (optimize control flow in TurboFan)
        type: bool  default: true
  --turbo-escape (enable escape analysis)
        type: bool  default: true
  --turbo-allocation-folding (Turbofan allocation folding)
        type: bool  default: true
  --turbo-instruction-scheduling (enable instruction scheduling in TurboFan)
        type: bool  default: false
  --turbo-stress-instruction-scheduling (randomly schedule instructions to stress dependency tracking)
        type: bool  default: false
  --turbo-store-elimination (enable store-store elimination in TurboFan)
        type: bool  default: true
  --trace-store-elimination (trace store elimination)
        type: bool  default: false
  --turbo-rewrite-far-jumps (rewrite far to near jumps (ia32,x64))
        type: bool  default: true
  --stress-gc-during-compilation (simulate GC/compiler thread race related to https://crbug.com/v8/8520)
        type: bool  default: false
  --turbo-fast-api-calls (enable fast API calls from TurboFan)
        type: bool  default: false
  --reuse-opt-code-count (don't discard optimized code for the specified number of deopts.)
        type: int  default: 0
  --turbo-nci (enable experimental native context independent code.)
        type: bool  default: false
  --turbo-nci-as-highest-tier (replace default TF with NCI code as the highest tier for testing purposes.)
        type: bool  default: false
  --print-nci-code (print native context independent code.)
        type: bool  default: false
  --trace-turbo-nci (trace native context independent code.)
        type: bool  default: false
  --turbo-collect-feedback-in-generic-lowering (enable experimental feedback collection in generic lowering.)
        type: bool  default: false
  --optimize-for-size (Enables optimizations which favor memory size over execution speed)
        type: bool  default: false
  --untrusted-code-mitigations (Enable mitigations for executing untrusted code)
        type: bool  default: false
  --expose-wasm (expose wasm interface to JavaScript)
        type: bool  default: true
  --assume-asmjs-origin (force wasm decoder to assume input is internal asm-wasm format)
        type: bool  default: false
  --wasm-num-compilation-tasks (maximum number of parallel compilation tasks for wasm)
        type: int  default: 128
  --wasm-write-protect-code-memory (write protect code memory on the wasm native heap)
        type: bool  default: false
  --wasm-async-compilation (enable actual asynchronous compilation for WebAssembly.compile)
        type: bool  default: true
  --wasm-test-streaming (use streaming compilation instead of async compilation for tests)
        type: bool  default: false
  --wasm-max-mem-pages (maximum initial number of 64KiB memory pages of a wasm instance)
        type: uint  default: 32767
  --wasm-max-mem-pages-growth (maximum number of 64KiB pages a Wasm memory can grow to)
        type: uint  default: 65536
  --wasm-max-table-size (maximum table size of a wasm instance)
        type: uint  default: 10000000
  --wasm-max-code-space (maximum committed code space for wasm (in MB))
        type: uint  default: 1024
  --wasm-tier-up (enable tier up to the optimizing compiler (requires --liftoff to have an effect))
        type: bool  default: true
  --trace-wasm-ast-start (start function for wasm AST trace (inclusive))
        type: int  default: 0
  --trace-wasm-ast-end (end function for wasm AST trace (exclusive))
        type: int  default: 0
  --liftoff (enable Liftoff, the baseline compiler for WebAssembly)
        type: bool  default: true
  --trace-wasm-memory (print all memory updates performed in wasm code)
        type: bool  default: false
  --wasm-tier-mask-for-testing (bitmask of functions to compile with TurboFan instead of Liftoff)
        type: int  default: 0
  --wasm-expose-debug-eval (Expose wasm evaluator support on the CDP)
        type: bool  default: false
  --validate-asm (validate asm.js modules before compiling)
        type: bool  default: true
  --suppress-asm-messages (don't emit asm.js related messages (for golden file testing))
        type: bool  default: false
  --trace-asm-time (log asm.js timing info to the console)
        type: bool  default: false
  --trace-asm-scanner (log tokens encountered by asm.js scanner)
        type: bool  default: false
  --trace-asm-parser (verbose logging of asm.js parse failures)
        type: bool  default: false
  --stress-validate-asm (try to validate everything as asm.js)
        type: bool  default: false
  --dump-wasm-module-path (directory to dump wasm modules to)
        type: string  default: nullptr
  --experimental-wasm-eh (enable prototype exception handling opcodes for wasm)
        type: bool  default: false
  --experimental-wasm-simd (enable prototype SIMD opcodes for wasm)
        type: bool  default: false
  --experimental-wasm-return-call (enable prototype return call opcodes for wasm)
        type: bool  default: false
  --experimental-wasm-compilation-hints (enable prototype compilation hints section for wasm)
        type: bool  default: false
  --experimental-wasm-gc (enable prototype garbage collection for wasm)
        type: bool  default: false
  --experimental-wasm-typed-funcref (enable prototype typed function references for wasm)
        type: bool  default: false
  --experimental-wasm-reftypes (enable prototype reference type opcodes for wasm)
        type: bool  default: false
  --experimental-wasm-threads (enable prototype thread opcodes for wasm)
        type: bool  default: false
  --experimental-wasm-type-reflection (enable prototype wasm type reflection in JS for wasm)
        type: bool  default: false
  --experimental-wasm-bigint (enable prototype JS BigInt support for wasm)
        type: bool  default: true
  --experimental-wasm-bulk-memory (enable prototype bulk memory opcodes for wasm)
        type: bool  default: true
  --experimental-wasm-mv (enable prototype multi-value support for wasm)
        type: bool  default: true
  --wasm-staging (enable staged wasm features)
        type: bool  default: false
  --wasm-opt (enable wasm optimization)
        type: bool  default: false
  --wasm-bounds-checks (enable bounds checks (disable for performance testing only))
        type: bool  default: true
  --wasm-stack-checks (enable stack checks (disable for performance testing only))
        type: bool  default: true
  --wasm-math-intrinsics (intrinsify some Math imports into wasm)
        type: bool  default: true
  --wasm-trap-handler (use signal handlers to catch out of bounds memory access in wasm (currently Linux x86_64 only))
        type: bool  default: true
  --wasm-fuzzer-gen-test (generate a test case when running a wasm fuzzer)
        type: bool  default: false
  --print-wasm-code (Print WebAssembly code)
        type: bool  default: false
  --print-wasm-stub-code (Print WebAssembly stub code)
        type: bool  default: false
  --asm-wasm-lazy-compilation (enable lazy compilation for asm-wasm modules)
        type: bool  default: false
  --wasm-lazy-compilation (enable lazy compilation for all wasm modules)
        type: bool  default: false
  --wasm-lazy-validation (enable lazy validation for lazily compiled wasm functions)
        type: bool  default: false
  --wasm-atomics-on-non-shared-memory (allow atomic operations on non-shared WebAssembly memory)
        type: bool  default: true
  --wasm-grow-shared-memory (allow growing shared WebAssembly memory objects)
        type: bool  default: true
  --wasm-simd-post-mvp (allow experimental SIMD operations for prototyping that are not included in the current proposal)
        type: bool  default: false
  --wasm-code-gc (enable garbage collection of wasm code)
        type: bool  default: true
  --trace-wasm-code-gc (trace garbage collection of wasm code)
        type: bool  default: false
  --stress-wasm-code-gc (stress test garbage collection of wasm code)
        type: bool  default: false
  --wasm-max-initial-code-space-reservation (maximum size of the initial wasm code space reservation (in MB))
        type: int  default: 0
  --frame-count (number of stack frames inspected by the profiler)
        type: int  default: 1
  --stress-sampling-allocation-profiler (Enables sampling allocation profiler with X as a sample interval)
        type: int  default: 0
  --lazy-new-space-shrinking (Enables the lazy new space shrinking strategy)
        type: bool  default: false
  --min-semi-space-size (min size of a semi-space (in MBytes), the new space consists of two semi-spaces)
        type: size_t  default: 0
  --max-semi-space-size (max size of a semi-space (in MBytes), the new space consists of two semi-spaces)
        type: size_t  default: 0
  --semi-space-growth-factor (factor by which to grow the new space)
        type: int  default: 2
  --max-old-space-size (max size of the old space (in Mbytes))
        type: size_t  default: 0
  --max-heap-size (max size of the heap (in Mbytes) both max_semi_space_size and max_old_space_size take precedence. All three flags cannot be specified at the same time.)
        type: size_t  default: 0
  --initial-heap-size (initial size of the heap (in Mbytes))
        type: size_t  default: 0
  --huge-max-old-generation-size (Increase max size of the old space to 4 GB for x64 systems withthe physical memory bigger than 16 GB)
        type: bool  default: true
  --initial-old-space-size (initial old space size (in Mbytes))
        type: size_t  default: 0
  --global-gc-scheduling (enable GC scheduling based on global memory)
        type: bool  default: true
  --gc-global (always perform global GCs)
        type: bool  default: false
  --random-gc-interval (Collect garbage after random(0, X) allocations. It overrides gc_interval.)
        type: int  default: 0
  --gc-interval (garbage collect after <n> allocations)
        type: int  default: -1
  --retain-maps-for-n-gc (keeps maps alive for <n> old space garbage collections)
        type: int  default: 2
  --trace-gc (print one trace line following each garbage collection)
        type: bool  default: false
  --trace-gc-nvp (print one detailed trace line in name=value format after each garbage collection)
        type: bool  default: false
  --trace-gc-ignore-scavenger (do not print trace line after scavenger collection)
        type: bool  default: false
  --trace-idle-notification (print one trace line following each idle notification)
        type: bool  default: false
  --trace-idle-notification-verbose (prints the heap state used by the idle notification)
        type: bool  default: false
  --trace-gc-verbose (print more details following each garbage collection)
        type: bool  default: false
  --trace-gc-freelists (prints details of each freelist before and after each major garbage collection)
        type: bool  default: false
  --trace-gc-freelists-verbose (prints details of freelists of each page before and after each major garbage collection)
        type: bool  default: false
  --trace-evacuation-candidates (Show statistics about the pages evacuation by the compaction)
        type: bool  default: false
  --trace-allocations-origins (Show statistics about the origins of allocations. Combine with --no-inline-new to track allocations from generated code)
        type: bool  default: false
  --trace-allocation-stack-interval (print stack trace after <n> free-list allocations)
        type: int  default: -1
  --trace-duplicate-threshold-kb (print duplicate objects in the heap if their size is more than given threshold)
        type: int  default: 0
  --trace-fragmentation (report fragmentation for old space)
        type: bool  default: false
  --trace-fragmentation-verbose (report fragmentation for old space (detailed))
        type: bool  default: false
  --minor-mc-trace-fragmentation (trace fragmentation after marking)
        type: bool  default: false
  --trace-evacuation (report evacuation statistics)
        type: bool  default: false
  --trace-mutator-utilization (print mutator utilization, allocation speed, gc speed)
        type: bool  default: false
  --incremental-marking (use incremental marking)
        type: bool  default: true
  --incremental-marking-wrappers (use incremental marking for marking wrappers)
        type: bool  default: true
  --incremental-marking-task (use tasks for incremental marking)
        type: bool  default: true
  --incremental-marking-soft-trigger (threshold for starting incremental marking via a task in percent of available space: limit - size)
        type: int  default: 0
  --incremental-marking-hard-trigger (threshold for starting incremental marking immediately in percent of available space: limit - size)
        type: int  default: 0
  --trace-unmapper (Trace the unmapping)
        type: bool  default: false
  --parallel-scavenge (parallel scavenge)
        type: bool  default: true
  --scavenge-task (schedule scavenge tasks)
        type: bool  default: true
  --scavenge-task-trigger (scavenge task trigger in percent of the current heap limit)
        type: int  default: 80
  --scavenge-separate-stack-scanning (use a separate phase for stack scanning in scavenge)
        type: bool  default: false
  --trace-parallel-scavenge (trace parallel scavenge)
        type: bool  default: false
  --write-protect-code-memory (write protect code memory)
        type: bool  default: true
  --concurrent-marking (use concurrent marking)
        type: bool  default: true
  --concurrent-array-buffer-sweeping (concurrently sweep array buffers)
        type: bool  default: true
  --concurrent-allocation (concurrently allocate in old space)
        type: bool  default: false
  --local-heaps (allow heap access from background tasks)
        type: bool  default: false
  --stress-concurrent-allocation (start background threads that allocate memory)
        type: bool  default: false
  --parallel-marking (use parallel marking in atomic pause)
        type: bool  default: true
  --ephemeron-fixpoint-iterations (number of fixpoint iterations it takes to switch to linear ephemeron algorithm)
        type: int  default: 10
  --trace-concurrent-marking (trace concurrent marking)
        type: bool  default: false
  --concurrent-store-buffer (use concurrent store buffer processing)
        type: bool  default: true
  --concurrent-sweeping (use concurrent sweeping)
        type: bool  default: true
  --parallel-compaction (use parallel compaction)
        type: bool  default: true
  --parallel-pointer-update (use parallel pointer update during compaction)
        type: bool  default: true
  --detect-ineffective-gcs-near-heap-limit (trigger out-of-memory failure to avoid GC storm near heap limit)
        type: bool  default: true
  --trace-incremental-marking (trace progress of the incremental marking)
        type: bool  default: false
  --trace-stress-marking (trace stress marking progress)
        type: bool  default: false
  --trace-stress-scavenge (trace stress scavenge progress)
        type: bool  default: false
  --track-gc-object-stats (track object counts and memory usage)
        type: bool  default: false
  --trace-gc-object-stats (trace object counts and memory usage)
        type: bool  default: false
  --trace-zone-stats (trace zone memory usage)
        type: bool  default: false
  --zone-stats-tolerance (report a tick only when allocated zone memory changes by this amount)
        type: size_t  default: 1048576
  --track-retaining-path (enable support for tracking retaining path)
        type: bool  default: false
  --concurrent-array-buffer-freeing (free array buffer allocations on a background thread)
        type: bool  default: true
  --gc-stats (Used by tracing internally to enable gc statistics)
        type: int  default: 0
  --track-detached-contexts (track native contexts that are expected to be garbage collected)
        type: bool  default: true
  --trace-detached-contexts (trace native contexts that are expected to be garbage collected)
        type: bool  default: false
  --move-object-start (enable moving of object starts)
        type: bool  default: true
  --memory-reducer (use memory reducer)
        type: bool  default: true
  --memory-reducer-for-small-heaps (use memory reducer for small heaps)
        type: bool  default: true
  --heap-growing-percent (specifies heap growing factor as (1 + heap_growing_percent/100))
        type: int  default: 0
  --v8-os-page-size (override OS page size (in KBytes))
        type: int  default: 0
  --always-compact (Perform compaction on every full GC)
        type: bool  default: false
  --never-compact (Never perform compaction on full GC - testing only)
        type: bool  default: false
  --compact-code-space (Compact code space on full collections)
        type: bool  default: true
  --flush-bytecode (flush of bytecode when it has not been executed recently)
        type: bool  default: true
  --stress-flush-bytecode (stress bytecode flushing)
        type: bool  default: false
  --use-marking-progress-bar (Use a progress bar to scan large objects in increments when incremental marking is active.)
        type: bool  default: true
  --stress-per-context-marking-worklist (Use per-context worklist for marking)
        type: bool  default: false
  --force-marking-deque-overflows (force overflows of marking deque by reducing it's size to 64 words)
        type: bool  default: false
  --stress-compaction (stress the GC compactor to flush out bugs (implies --force_marking_deque_overflows))
        type: bool  default: false
  --stress-compaction-random (Stress GC compaction by selecting random percent of pages as evacuation candidates. It overrides stress_compaction.)
        type: bool  default: false
  --stress-incremental-marking (force incremental marking for small heaps and run it more often)
        type: bool  default: false
  --fuzzer-gc-analysis (prints number of allocations and enables analysis mode for gc fuzz testing, e.g. --stress-marking, --stress-scavenge)
        type: bool  default: false
  --stress-marking (force marking at random points between 0 and X (inclusive) percent of the regular marking start limit)
        type: int  default: 0
  --stress-scavenge (force scavenge at random points between 0 and X (inclusive) percent of the new space capacity)
        type: int  default: 0
  --gc-experiment-background-schedule (new background GC schedule heuristics)
        type: bool  default: false
  --gc-experiment-less-compaction (less compaction in non-memory reducing mode)
        type: bool  default: false
  --disable-abortjs (disables AbortJS runtime function)
        type: bool  default: false
  --randomize-all-allocations (randomize virtual memory reservations by ignoring any hints passed when allocating pages)
        type: bool  default: false
  --manual-evacuation-candidates-selection (Test mode only flag. It allows an unit test to select evacuation candidates pages (requires --stress_compaction).)
        type: bool  default: false
  --fast-promotion-new-space (fast promote new space on high survival rates)
        type: bool  default: false
  --clear-free-memory (initialize free memory with 0)
        type: bool  default: false
  --young-generation-large-objects (allocates large objects by default in the young generation large object space)
        type: bool  default: true
  --debug-code (generate extra code (assertions) for debugging)
        type: bool  default: false
  --code-comments (emit comments in code disassembly; for more readable source positions you should add --no-concurrent_recompilation)
        type: bool  default: false
  --enable-sse3 (enable use of SSE3 instructions if available)
        type: bool  default: true
  --enable-ssse3 (enable use of SSSE3 instructions if available)
        type: bool  default: true
  --enable-sse4-1 (enable use of SSE4.1 instructions if available)
        type: bool  default: true
  --enable-sse4-2 (enable use of SSE4.2 instructions if available)
        type: bool  default: true
  --enable-sahf (enable use of SAHF instruction if available (X64 only))
        type: bool  default: true
  --enable-avx (enable use of AVX instructions if available)
        type: bool  default: true
  --enable-fma3 (enable use of FMA3 instructions if available)
        type: bool  default: true
  --enable-bmi1 (enable use of BMI1 instructions if available)
        type: bool  default: true
  --enable-bmi2 (enable use of BMI2 instructions if available)
        type: bool  default: true
  --enable-lzcnt (enable use of LZCNT instruction if available)
        type: bool  default: true
  --enable-popcnt (enable use of POPCNT instruction if available)
        type: bool  default: true
  --arm-arch (generate instructions for the selected ARM architecture if available: armv6, armv7, armv7+sudiv or armv8)
        type: string  default: armv8
  --force-long-branches (force all emitted branches to be in long mode (MIPS/PPC only))
        type: bool  default: false
  --mcpu (enable optimization for specific cpu)
        type: string  default: auto
  --partial-constant-pool (enable use of partial constant pools (X64 only))
        type: bool  default: true
  --sim-arm64-optional-features (enable optional features on the simulator for testing: none or all)
        type: string  default: none
  --enable-source-at-csa-bind (Include source information in the binary at CSA bind locations.)
        type: bool  default: false
  --enable-armv7 (deprecated (use --arm_arch instead))
        type: maybe_bool  default: unset
  --enable-vfp3 (deprecated (use --arm_arch instead))
        type: maybe_bool  default: unset
  --enable-32dregs (deprecated (use --arm_arch instead))
        type: maybe_bool  default: unset
  --enable-neon (deprecated (use --arm_arch instead))
        type: maybe_bool  default: unset
  --enable-sudiv (deprecated (use --arm_arch instead))
        type: maybe_bool  default: unset
  --enable-armv8 (deprecated (use --arm_arch instead))
        type: maybe_bool  default: unset
  --enable-regexp-unaligned-accesses (enable unaligned accesses for the regexp engine)
        type: bool  default: true
  --script-streaming (enable parsing on background)
        type: bool  default: true
  --stress-background-compile (stress test parsing on background)
        type: bool  default: false
  --finalize-streaming-on-background (perform the script streaming finalization on the background thread)
        type: bool  default: false
  --disable-old-api-accessors (Disable old-style API accessors whose setters trigger through the prototype chain)
        type: bool  default: false
  --expose-gc (expose gc extension)
        type: bool  default: false
  --expose-gc-as (expose gc extension under the specified name)
        type: string  default: nullptr
  --expose-externalize-string (expose externalize string extension)
        type: bool  default: false
  --expose-trigger-failure (expose trigger-failure extension)
        type: bool  default: false
  --stack-trace-limit (number of stack frames to capture)
        type: int  default: 10
  --builtins-in-stack-traces (show built-in functions in stack traces)
        type: bool  default: false
  --experimental-stack-trace-frames (enable experimental frames (API/Builtins) and stack trace layout)
        type: bool  default: false
  --disallow-code-generation-from-strings (disallow eval and friends)
        type: bool  default: false
  --expose-async-hooks (expose async_hooks object)
        type: bool  default: false
  --expose-cputracemark-as (expose cputracemark extension under the specified name)
        type: string  default: nullptr
  --allow-unsafe-function-constructor (allow invoking the function constructor without security checks)
        type: bool  default: false
  --force-slow-path (always take the slow path for builtins)
        type: bool  default: false
  --test-small-max-function-context-stub-size (enable testing the function context size overflow path by making the maximum size smaller)
        type: bool  default: false
  --inline-new (use fast inline allocation)
        type: bool  default: true
  --trace (trace javascript function calls)
        type: bool  default: false
  --trace-wasm (trace wasm function calls)
        type: bool  default: false
  --lazy (use lazy compilation)
        type: bool  default: true
  --max-lazy (ignore eager compilation hints)
        type: bool  default: false
  --trace-opt (trace lazy optimization)
        type: bool  default: false
  --trace-opt-verbose (extra verbose compilation tracing)
        type: bool  default: false
  --trace-opt-stats (trace lazy optimization statistics)
        type: bool  default: false
  --trace-deopt (trace optimize function deoptimization)
        type: bool  default: false
  --trace-file-names (include file names in trace-opt/trace-deopt output)
        type: bool  default: false
  --always-opt (always try to optimize functions)
        type: bool  default: false
  --always-osr (always try to OSR functions)
        type: bool  default: false
  --prepare-always-opt (prepare for turning on always opt)
        type: bool  default: false
  --trace-serializer (print code serializer trace)
        type: bool  default: false
  --compilation-cache (enable compilation cache)
        type: bool  default: true
  --cache-prototype-transitions (cache prototype transitions)
        type: bool  default: true
  --parallel-compile-tasks (enable parallel compile tasks)
        type: bool  default: false
  --compiler-dispatcher (enable compiler dispatcher)
        type: bool  default: false
  --trace-compiler-dispatcher (trace compiler dispatcher activity)
        type: bool  default: false
  --cpu-profiler-sampling-interval (CPU profiler sampling interval in microseconds)
        type: int  default: 1000
  --trace-side-effect-free-debug-evaluate (print debug messages for side-effect-free debug-evaluate for testing)
        type: bool  default: false
  --hard-abort (abort by crashing)
        type: bool  default: true
  --expose-inspector-scripts (expose injected-script-source.js for debugging)
        type: bool  default: false
  --stack-size (default size of stack region v8 is allowed to use (in kBytes))
        type: int  default: 984
  --max-stack-trace-source-length (maximum length of function source code printed in a stack trace.)
        type: int  default: 300
  --clear-exceptions-on-js-entry (clear pending exceptions when entering JavaScript)
        type: bool  default: false
  --histogram-interval (time interval in ms for aggregating memory histograms)
        type: int  default: 600000
  --heap-profiler-trace-objects (Dump heap object allocations/movements/size_updates)
        type: bool  default: false
  --heap-profiler-use-embedder-graph (Use the new EmbedderGraph API to get embedder nodes)
        type: bool  default: true
  --heap-snapshot-string-limit (truncate strings to this length in the heap snapshot)
        type: int  default: 1024
  --sampling-heap-profiler-suppress-randomness (Use constant sample intervals to eliminate test flakiness)
        type: bool  default: false
  --use-idle-notification (Use idle notification to reduce memory footprint.)
        type: bool  default: true
  --trace-ic (trace inline cache state transitions for tools/ic-processor)
        type: bool  default: false
  --modify-field-representation-inplace (enable in-place field representation updates)
        type: bool  default: true
  --max-polymorphic-map-count (maximum number of maps to track in POLYMORPHIC state)
        type: int  default: 4
  --native-code-counters (generate extra code for manipulating stats counters)
        type: bool  default: false
  --thin-strings (Enable ThinString support)
        type: bool  default: true
  --trace-prototype-users (Trace updates to prototype user tracking)
        type: bool  default: false
  --trace-for-in-enumerate (Trace for-in enumerate slow-paths)
        type: bool  default: false
  --trace-maps (trace map creation)
        type: bool  default: false
  --trace-maps-details (also log map details)
        type: bool  default: true
  --allow-natives-syntax (allow natives syntax)
        type: bool  default: false
  --allow-natives-for-differential-fuzzing (allow only natives explicitly allowlisted for differential fuzzers)
        type: bool  default: false
  --parse-only (only parse the sources)
        type: bool  default: false
  --trace-sim (Trace simulator execution)
        type: bool  default: false
  --debug-sim (Enable debugging the simulator)
        type: bool  default: false
  --check-icache (Check icache flushes in ARM and MIPS simulator)
        type: bool  default: false
  --stop-sim-at (Simulator stop after x number of instructions)
        type: int  default: 0
  --sim-stack-alignment (Stack alignment in bytes in simulator (4 or 8, 8 is default))
        type: int  default: 8
  --sim-stack-size (Stack size of the ARM64, MIPS64 and PPC64 simulator in kBytes (default is 2 MB))
        type: int  default: 2048
  --log-colour (When logging, try to use coloured output.)
        type: bool  default: true
  --trace-sim-messages (Trace simulator debug messages. Implied by --trace-sim.)
        type: bool  default: false
  --async-stack-traces (include async stack traces in Error.stack)
        type: bool  default: true
  --stack-trace-on-illegal (print stack trace when an illegal exception is thrown)
        type: bool  default: false
  --abort-on-uncaught-exception (abort program (dump core) when an uncaught exception is thrown)
        type: bool  default: false
  --correctness-fuzzer-suppressions (Suppress certain unspecified behaviors to ease correctness fuzzing: Abort program when the stack overflows or a string exceeds maximum length (as opposed to throwing RangeError). Use a fixed suppression string for error messages.)
        type: bool  default: false
  --randomize-hashes (randomize hashes to avoid predictable hash collisions (with snapshots this option cannot override the baked-in seed))
        type: bool  default: true
  --rehash-snapshot (rehash strings from the snapshot to override the baked-in seed)
        type: bool  default: true
  --hash-seed (Fixed seed to use to hash property keys (0 means random)(with snapshots this option cannot override the baked-in seed))
        type: uint64  default: 0
  --random-seed (Default seed for initializing random generator (0, the default, means to use system random).)
        type: int  default: 0
  --fuzzer-random-seed (Default seed for initializing fuzzer random generator (0, the default, means to use v8's random number generator seed).)
        type: int  default: 0
  --trace-rail (trace RAIL mode)
        type: bool  default: false
  --print-all-exceptions (print exception object and stack trace on each thrown exception)
        type: bool  default: false
  --detailed-error-stack-trace (includes arguments for each function call in the error stack frames array)
        type: bool  default: false
  --adjust-os-scheduling-parameters (adjust OS specific scheduling params for the isolate)
        type: bool  default: true
  --runtime-call-stats (report runtime call counts and times)
        type: bool  default: false
  --rcs (report runtime call counts and times)
        type: bool  default: false
  --rcs-cpu-time (report runtime times in cpu time (the default is wall time))
        type: bool  default: false
  --profile-deserialization (Print the time it takes to deserialize the snapshot.)
        type: bool  default: false
  --serialization-statistics (Collect statistics on serialized objects.)
        type: bool  default: false
  --serialization-chunk-size (Custom size for serialization chunks)
        type: uint  default: 4096
  --regexp-optimization (generate optimized regexp code)
        type: bool  default: true
  --regexp-mode-modifiers (enable inline flags in regexp.)
        type: bool  default: false
  --regexp-interpret-all (interpret all regexp code)
        type: bool  default: false
  --regexp-tier-up (enable regexp interpreter and tier up to the compiler after the number of executions set by the tier up ticks flag)
        type: bool  default: true
  --regexp-tier-up-ticks (set the number of executions for the regexp interpreter before tiering-up to the compiler)
        type: int  default: 1
  --regexp-peephole-optimization (enable peephole optimization for regexp bytecode)
        type: bool  default: true
  --trace-regexp-peephole-optimization (trace regexp bytecode peephole optimization)
        type: bool  default: false
  --trace-regexp-bytecodes (trace regexp bytecode execution)
        type: bool  default: false
  --trace-regexp-assembler (trace regexp macro assembler calls.)
        type: bool  default: false
  --trace-regexp-parser (trace regexp parsing)
        type: bool  default: false
  --trace-regexp-tier-up (trace regexp tiering up execution)
        type: bool  default: false
  --testing-bool-flag (testing_bool_flag)
        type: bool  default: true
  --testing-maybe-bool-flag (testing_maybe_bool_flag)
        type: maybe_bool  default: unset
  --testing-int-flag (testing_int_flag)
        type: int  default: 13
  --testing-float-flag (float-flag)
        type: float  default: 2.5
  --testing-string-flag (string-flag)
        type: string  default: Hello, world!
  --testing-prng-seed (Seed used for threading test randomness)
        type: int  default: 42
  --testing-d8-test-runner (test runner turns on this flag to enable a check that the function was prepared for optimization before marking it for optimization)
        type: bool  default: false
  --fuzzing (Fuzzers use this flag to signal that they are ... fuzzing. This causes intrinsics to fail silently (e.g. return undefined) on invalid usage.)
        type: bool  default: false
  --embedded-src (Path for the generated embedded data file. (mksnapshot only))
        type: string  default: nullptr
  --embedded-variant (Label to disambiguate symbols in embedded data file. (mksnapshot only))
        type: string  default: nullptr
  --startup-src (Write V8 startup as C++ src. (mksnapshot only))
        type: string  default: nullptr
  --startup-blob (Write V8 startup blob file. (mksnapshot only))
        type: string  default: nullptr
  --target-arch (The mksnapshot target arch. (mksnapshot only))
        type: string  default: nullptr
  --target-os (The mksnapshot target os. (mksnapshot only))
        type: string  default: nullptr
  --target-is-simulator (Instruct mksnapshot that the target is meant to run in the simulator and it can generate simulator-specific instructions. (mksnapshot only))
        type: bool  default: false
  --minor-mc-parallel-marking (use parallel marking for the young generation)
        type: bool  default: true
  --trace-minor-mc-parallel-marking (trace parallel marking for the young generation)
        type: bool  default: false
  --minor-mc (perform young generation mark compact GCs)
        type: bool  default: false
  --help (Print usage message, including flags, on console)
        type: bool  default: true
  --dump-counters (Dump counters on exit)
        type: bool  default: false
  --dump-counters-nvp (Dump counters as name-value pairs on exit)
        type: bool  default: false
  --use-external-strings (Use external strings for source code)
        type: bool  default: false
  --map-counters (Map counters to a file)
        type: string  default:
  --mock-arraybuffer-allocator (Use a mock ArrayBuffer allocator for testing.)
        type: bool  default: false
  --mock-arraybuffer-allocator-limit (Memory limit for mock ArrayBuffer allocator used to simulate OOM for testing.)
        type: size_t  default: 0
  --gdbjit (enable GDBJIT interface)
        type: bool  default: false
  --gdbjit-full (enable GDBJIT interface for all code objects)
        type: bool  default: false
  --gdbjit-dump (dump elf objects with debug info to disk)
        type: bool  default: false
  --gdbjit-dump-filter (dump only objects containing this substring)
        type: string  default:
  --log (Minimal logging (no API, code, GC, suspect, or handles samples).)
        type: bool  default: false
  --log-all (Log all events to the log file.)
        type: bool  default: false
  --log-api (Log API events to the log file.)
        type: bool  default: false
  --log-code (Log code events to the log file without profiling.)
        type: bool  default: false
  --log-handles (Log global handle events.)
        type: bool  default: false
  --log-suspect (Log suspect operations.)
        type: bool  default: false
  --log-source-code (Log source code.)
        type: bool  default: false
  --log-function-events (Log function events (parse, compile, execute) separately.)
        type: bool  default: false
  --prof (Log statistical profiling information (implies --log-code).)
        type: bool  default: false
  --detailed-line-info (Always generate detailed line information for CPU profiling.)
        type: bool  default: false
  --prof-sampling-interval (Interval for --prof samples (in microseconds).)
        type: int  default: 1000
  --prof-cpp (Like --prof, but ignore generated code.)
        type: bool  default: false
  --prof-browser-mode (Used with --prof, turns on browser-compatible mode for profiling.)
        type: bool  default: true
  --logfile (Specify the name of the log file.)
        type: string  default: v8.log
  --logfile-per-isolate (Separate log files for each isolate.)
        type: bool  default: true
  --ll-prof (Enable low-level linux profiler.)
        type: bool  default: false
  --gc-fake-mmap (Specify the name of the file for fake gc mmap used in ll_prof)
        type: string  default: /tmp/__v8_gc__
  --log-internal-timer-events (Time internal events.)
        type: bool  default: false
  --redirect-code-traces (output deopt information and disassembly into file code-<pid>-<isolate id>.asm)
        type: bool  default: false
  --redirect-code-traces-to (output deopt information and disassembly into the given file)
        type: string  default: nullptr
  --print-opt-source (print source code of optimized and inlined functions)
        type: bool  default: false
  --vtune-prof-annotate-wasm (Used when v8_enable_vtunejit is enabled, load wasm source map and provide annotate support (experimental).)
        type: bool  default: false
  --win64-unwinding-info (Enable unwinding info for Windows/x64)
        type: bool  default: true
  --interpreted-frames-native-stack (Show interpreted frames on the native stack (useful for external profilers).)
        type: bool  default: false
  --predictable (enable predictable mode)
        type: bool  default: false
  --predictable-gc-schedule (Predictable garbage collection schedule. Fixes heap growing, idle, and memory reducing behavior.)
        type: bool  default: false
  --single-threaded (disable the use of background tasks)
        type: bool  default: false
  --single-threaded-gc (disable the use of background gc tasks)
        type: bool  default: false

Particularly useful ones:

--async-stack-trace