What the Go scheduler does when your goroutine blocks
A blocking syscall costs an OS thread. A blocking network read costs nothing. Measured with 200 goroutines, GOMAXPROCS=2 and a thread count.
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The GOGC I set next to GOMEMLIMIT never fired
GOGC=100 with a 256 MiB limit produced exactly what GOGC=off produced: same collections, same CPU share, same throughput. The tighter rule binds, the other goes quiet.
- Ecosystem and tooling
A 404 from net/http costs 62 allocations
A static route through net/http's mux costs 85.6 ns and nothing on the heap. A path that matches no pattern costs 2125.5 ns and 62 allocations.
- Concurrency in practice
The mutex was 68 times faster, until I added work
One goroutine: 2.5 ns for the mutex, 172.6 ns for the channel. Sixteen goroutines with real work: the channel wins by less than the harness's own error.
- Runtime internals
A 1 MiB goroutine stack costs 136µs and reports 144 B/op
Reaching a 1 MiB stack copied it nine times. The copying cost 136µs of CPU that -benchmem reports as 144 bytes, because stack memory is not heap memory.
- Performance and measurement
benchstat reported p=0.000 between a function and itself
Two sub-benchmarks calling the same function with the same argument came back 1.10% apart at p=0.000. What a benchmark measures is not only your code.
- Runtime internals
GOMAXPROCS is not your thread count
GOMAXPROCS=1 with 200 goroutines blocked in read(2) produced 202 OS threads. Measured on go1.27.0, alongside the container case Go 1.25 changed.
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