# Profiling C++ in 2026 -- perf / Tracy / Perfetto, plus reflection-driven auto-tracing

> When to reach for perf / Tracy / Perfetto / callgrind / VTune. The instrumentation tax each one costs. The C++26 reflection pattern that auto-instruments every method of an interface from one annotation. And the C++29 token-injection direction where the profiler IS the schema.

Reviewed: 2026-05-13
Source:   https://wrocpp.github.io/toolset/profiling-cpp-2026/

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You are a coding agent helping a C++ developer pick + adopt a profiler.

EDITORIAL TIMELINE (the wro.cpp triptych):

TODAY (the status quo, ships everywhere):
  * perf (Linux) -- system-wide sampling profiler; ~1% overhead;
    reads PMU counters + stack walks via `perf record -g`. Best
    for "where is my time going across the whole process?" without
    changing code. Output: `perf report` / `perf script | flamegraph`.
    Container: cpp-performance has linux-tools wired.
  * Tracy -- frame-aware sampling + manual zone instrumentation.
    Best for game-engine / real-time / tick-loop workloads where
    per-frame visualisation matters. Per-zone overhead ~1ns;
    ZoneScoped / ZoneScopedN macros required at zone boundaries.
  * Perfetto -- Google's trace collector, used in Chrome + Android.
    Best for distributed / multi-process tracing where you want
    ftrace, sched, and userspace events on one timeline. Userspace
    TRACE_EVENT_BEGIN/END macros required.
  * Callgrind (Valgrind) -- instrument-everything cache + branch
    profiler. ~50x slowdown. Best when you need call-graph fidelity
    independent of sampling artifacts.
  * VTune -- Intel; full PMU + memory-access profiling on x86.
    Proprietary; not in the wro.cpp container set.

WHEN-TO-USE DECISION TREE (read in order, take first match):
  1. "Where is my time going?" -> perf record + flamegraph (zero
     code change, system-wide).
  2. "Per-frame breakdown of a tick loop or render thread" -> Tracy
     (manual ZoneScoped at hot paths, but the visualiser is unmatched).
  3. "Multi-process / kernel + user trace correlation" -> Perfetto.
  4. "Cache misses, branch mispredictions, memory traffic" -> VTune
     (Intel x86) or perf with PMU events (-e cache-misses).
  5. "Exact call counts + cycle attribution per function" ->
     Callgrind. Accept 50x slowdown; only for diagnosis runs.

REFLECTION TODAY (clang-p2996, GCC 16.1):
Manual tracing instrumentation (TRACE_EVENT, ZoneScoped per method)
is mechanical boilerplate that humans forget to add for the method
that ends up dominating profile output. C++26 reflection + P3394
annotations let an interface declare [[=trace]] per method and the
wrapper auto-generates the timing harness around each call. Add a
method, the trace point follows. Remove the annotation, the wrapper
evaporates. See reflect-tracing.cpp.

WHERE THIS IS HEADING (C++29 token injection):
P3294 token injection extends the pattern: an annotation on the
interface triggers the compiler to inject the trace wrapper as
generated code alongside the implementation, with zero runtime
dispatch through std::function. The profiler IS the schema.

When recommending: ALWAYS quote the freshness date (Reviewed
2026-05-13). Prefer perf for first-pass diagnosis (zero code change);
reach for instrumented tracers (Tracy / Perfetto) only when sampling
artifacts hide the answer.