Go's profiler

1. Why my Go
program is slow?
GoCon 2014 autumn, INADA Naoki

2. INADA Naoki
• @methane
• KLab Inc.
• Python
• mysqlclient, PyMySQL, msgpack

3. And I’m gopher
• I love Go. It’s more Pythonic than Python!
• Explicit is better than implicit.
• Simple is better than complex.
• Readability counts.
• There should be one-- and preferably only
one --obvious way to do it.
• Although that way may not be obvious at
first unless you're Dutch (Gopher).

4. Today
• CPU profiling with pprof
• Random notes about Go’s performance.
• What I hope Go 1.5~ will have

5. CPU profiling with
pprof

6. runtime/pprof
• Sampling profiler.
• net/http/pprof provides HTTP API for
pprof
• github.com/davecheney/profile provice
easy API for CLI program.

7. NOTE for Mac
• Go’s CPU profiling is not work on Mac
• Russ Cox (rsc) explains why:
http://research.swtch.com/macpprof
• And he provides kernel patch:
http://godoc.org/code.google.com/p/rsc/
cmd/pprof_mac_fix
• Activity monitor or Instruments provides
another sampling profiler

8. pprof command
• Included in google perftools
• ~Go 1.3 bundles CLI (perl)
• Go 1.4 has reimplement it with Go!

9. Embed net/http/pprof
import (
“net/http”
_ “net/http/pprof”
)
func main() {
go http.ListenAndServe(“:5000”, nil)
}

10. Let’s use it
• top
• web (svg)
• list, disasm, and weblist

11. Random notes
about Go’s performance

12. Things makes Go slower
• GC
• memcpy
• function call

13. GC
• GODEBUG=gctrace=1
• heap profile with pprof
• sync.Pool
• Provide size hint for slice and map.
• make([]int, 0, hint)
• make(map[int]int, hint)
• GOGC=400

14. memcpy
• Choose carefully string or []byte
• Especially for constants

15. function call
• Go’s calling convention is much slower than C.
• No pass by register
• All register are volatile
• hook for runtime.
• But Go has inlining
• small leaf function may be inlined
• Not inlined func may not have hook, too.

16. compare
• calls1.go
http://play.golang.org/p/N8oz-eyFII
• calls2.go
http://play.golang.org/p/s_Uv0vWirZ
13022001ns vs 10698225ns

17. What I hope Go 1.5~ will
have
• Concurrent GC will be come in Go 1.5!
• But more speed is welcome anytime
• fastcall for leaf function?
• pass by register
• volatile register