You, latency and profiling @ GolangUK 2017

Transcript

1. You, latency and profiling
   Filippo Valsorda — @FiloSo/le
   

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2. What is fast?
   

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3. A fast hash…
   … can hash many MB per second
   

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4. A fast regex…
   … can process many MB/s
   

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5. A fast database…
   … can store many GB per second
   

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6. A fast database…
   … can store many GB per second
   … or replies to queries in a few ms
   

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7. A fast website…
   … can handle many requests
   … or loads in a few milliseconds
   

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8. A fast API…
   … can handle many clients
   … or answers in a few milliseconds
   

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9. Fast is…
   Throughput
   and
   Latency
   

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10. CPU profiling
    -cpuprofile
    

    /debug/pprof/profile
    

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11. SIGPROF
    CPU profiling
    

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12. runtime/proc.go
    

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13. h>p.Handler 1
    Running on CPU
    h>p.Handler 2
    I/O
    I/O
    h>p.Handler 3 I/O
    h>p.Handler 4 I/O
    CPU profiling
    

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14. Running on CPU
    I/O
    I/O
    I/O
    I/O
    h>p.Handler 1
    h>p.Handler 2
    h>p.Handler 3
    h>p.Handler 4
    CPU profiling
    

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15. I/O
    Observed latency
    h>p.Handler 1
    CPU profiling
    

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16. func Write(data []byte) {
    for i := 0; i < 50; i++ {
    tmpfile, _ := ioutil.TempFile("", "ex")
    defer os.Remove(tmpfile.Name())
    _, err = tmpfile.Write(data)
    tmpfile.Close()
    }
    }
    func Hash(data []byte) {
    for i := 0; i < 50; i++ {
    sha256.Sum256(data)
    }
    }
    

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17. $ time curl http://127.0.0.1:12345/hash-and-write

    9.831 total

    go tool pprof -web slowserver cpu.pprof
    

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19. $ time curl http://127.0.0.1:12345/hash-and-write

    9.831 total

    

    

    $ time curl http://127.0.0.1:12345/write-no-hash

    7.692 total
    

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20. Latency
    is not all about CPU
    

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21. CPU profiling is for throughput
    The tracer is for latency
    

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22. $ time curl http://127.0.0.1:12345/write-no-hash

    7.692 total

    go tool trace -pprof=syscall trace.out > syscall.pprof
    go tool pprof -web syscall.pprof
    

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24. The tracer
    Detailed nanosecond-level log of
    execuOon events:
    • gorouOne scheduling, blocking
    • syscalls, network, I/O
    • garbage collecOon
    

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25. •log files are BIG
    •25% overhead (aWer Go 1.7)
    •symbols are embedded (Go 1.7)
    The tracer
    

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26. •Full event context
    •GorouOne metadata and history
    •Discrete events, not samples
    Trace vs. profile
    

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27. CPU profiling
    Total: 20 samples
    

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28. Tracing events
    

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29. import "runtime/trace"
    

    import "net/http/pprof"
    /debug/pprof/trace?seconds=5
    The tracer
    

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31. go tool trace -pprof=TYPE trace.out
    Supported profile types are:
    - net: network blocking profile
    - sync: synchronization blocking profile
    - syscall: syscall blocking profile
    - sched: scheduler latency profile
    

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32. go tool trace -pprof=syscall trace.out
    > syscall.pprof
    go tool pprof -web syscall.pprof
    

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33. go tool trace -pprof=syscall trace.out
    > syscall.pprof
    go-torch -b syscall.pprof && 

    open torch.svg
    

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36. -pprof=syscall
    func Write(data []byte) {
    for i := 0; i < 50; i++ {
    tmpfile, _ := ioutil.TempFile("", "ex")
    defer os.Remove(tmpfile.Name())
    _, err = tmpfile.Write(data)
    tmpfile.Close()
    }
    }
    

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37. -pprof=sync
    // Block waits on a channel
    func Block() {
    }
    

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38. -pprof=sync
    

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39. -pprof=sync
    

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40. -pprof=net
    func Download() []byte {
    r, err := http.Get("https://golang.org/doc/go1.8")
    body, err := ioutil.ReadAll(r.Body)
    r.Body.Close()
    return body
    }
    

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41. -pprof=net
    

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42. -pprof=net
    

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43. -pprof=net
    

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45. WriIng our own profile
    prof := make(map[uint64]pprof.Record)
    for _, ev := range events {
    if ev.Type != trace.EvGoBlockNet {
    continue
    }
    rec := prof[ev.StkID]
    rec.Stk = ev.Stk
    rec.N++
    rec.Time += ev.Link.Ts - ev.Ts
    prof[ev.StkID] = rec
    }
    pprof.BuildProfile(prof).Write(os.Stdout)
    

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46. var childG = make(map[uint64]struct{})
    var lastGLen int
    for {
    for _, ev := range events {
    if ev.Type != trace.EvGoCreate {
    continue
    }
    if _, ok := childG[ev.G]; !ok && !filterStack(ev.Stk, re) {
    continue
    }
    childG[ev.Args[0]] = struct{}{}
    }
    if len(childG) == lastGLen {
    break
    }
    lastGLen = len(childG)
    }
    

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47. tracefocus
    tracefocus -filter=ServeHTTP trace.out >
    net.pprof

    

    github.com/FiloSottile/tracetools
    

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50. Build more tools!
    • Focus on gorouOne number
    • Aggregate all blocking types
    • VisualizaOons
    • …
    

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51. tracehist

    tracehist -filter=Close trace.out 

    

    github.com/FiloSottile/tracetools
    

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53. Build more tools!
    Profile latency!
    

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54. QuesIons?
    Filippo Valsorda
    @FiloSo/le
    hi@filippo.io
    

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