traceparse

traceparse summarizes GC activity from Go execution trace files (.trace.out) produced by go test -trace or the -perf-trace flag in scheduler_perf.

Usage

go -C hack/tools build -o /tmp/traceparse ./traceparse
/tmp/traceparse <trace-file> [<trace-file> ...]

Output

For each file the tool prints a table of named range events sorted by total wall-clock duration, followed by the average live heap size:

=== path/to/foo-trace.out ===
range                                                    count  total duration
-----                                                    -----  --------------
GC concurrent mark phase                                    47  5.662s
GC mark assist                                           14294  743.936ms
GC incremental sweep                                    161077  321.769ms
stop-the-world (GC sweep termination)                       47  7.568ms
stop-the-world (read mem stats)                             42  5.446ms
stop-the-world (GC mark termination)                        47  2.221ms
stop-the-world (start trace)                                 1  1.792µs

avg live heap: 796 MB  (3827825 samples)

Key metrics for scheduler_perf analysis

Range	What it tells you
`GC concurrent mark phase`	Total GC work; fewer cycles / less time = less allocation pressure
`GC mark assist`	Most sensitive indicator: goroutines interrupted mid-scheduling to help mark because allocation outpaces background GC; high counts mean hot-path allocations are limiting throughput
`stop-the-world (GC sweep termination)`	STW pauses that stop all goroutines; directly affects scheduling tail latency
`stop-the-world (GC mark termination)`	Second STW pause per cycle; usually short
`avg live heap`	Working set size; drives GC trigger frequency