I am pretty sure that a "proc" in the trace visualization output is the
same as a "P" in the parlance of the Go runtime scheduler. In the scheduler
an OS thread is an "M" and even when using LockOSThread the locked
goroutine and thread need to be paired up with one of the scheduler's Ps in
order to execute the goroutine's code. There are always GOMAXPROCS # of Ps
in the scheduler. See the comment block starting at line 19 in this code
for more detail. https://golang.org/src/runtime/proc.go
Hope that helps,
Chris
On Sunday, October 6, 2019 at 7:47:43 AM UTC-4, Miki Tebeka wrote:
>
> Hi,
>
> I'm trying to understand output of the "go tool trace". I'm using
> runtime.LockOSThread, however the output of the trace tool shows goroutines
> moving between procs (which I *think* are OS threads). What am I missing?
>
> Code:
> package main
>
> import (
> "fmt"
> "os"
> "runtime"
> "runtime/trace"
> "time"
> )
>
> func sqrt(val float64) (float64, error) {
> if val < 0.0 {
> return 0.0, fmt.Errorf("sqrt of negative number")
> }
>
> if val == 0.0 {
> return 0.0, nil // shortcut
> }
>
> guess, epsilon := 1.0, 0.00001
> for i := 0; i < 10000; i++ {
> diff := guess*guess - val
> if diff < 0 {
> diff = -diff
> }
> if diff <= epsilon {
> return guess, nil
> }
> guess = (val/guess + guess) / 2.0
> }
>
> return 0.0, fmt.Errorf("can't find sqrt of %f", val)
> }
>
> func worker(id int) {
> runtime.LockOSThread()
> i := float64(0)
> for {
> for n := 0; n < 1000000; n++ {
> i += 13.2
> _, err := sqrt(i)
> if err != nil {
> panic(err)
> }
> }
> runtime.Gosched()
> }
> }
>
> func main() {
> out, err := os.Create("trace.out")
> if err != nil {
> panic(err)
> }
> defer out.Close()
> if err := trace.Start(out); err != nil {
> panic(err)
> }
> defer trace.Stop()
>
> for i := 0; i < runtime.NumCPU(); i++ {
> go worker(i)
> }
>
> time.Sleep(3 * time.Second)
> }
>
>
> What I see in trace:
>
> [image: trace-out.png]
>
> Thanks,
> Miki
>
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