Commit d0736775 authored by Dave Cheney's avatar Dave Cheney

cgo/misc/test: burn CPU to improve sleep accuracy

Fixes #4008.

Run a background goroutine that wastes CPU to trick the
power management into raising the CPU frequency which,
by side effect, makes sleep more accurate on arm.

=== RUN TestParallelSleep
--- PASS: TestParallelSleep (1.30 seconds)
_cgo_gotypes.go:772:    sleep(1) slept for 1.000458s

R=minux.ma, r
CC=golang-dev
https://golang.org/cl/6498060
parent 11d75fb6
......@@ -35,16 +35,35 @@ func BackgroundSleep(n int) {
}()
}
// wasteCPU starts a background goroutine to waste CPU
// to cause the power management to raise the CPU frequency.
// On ARM this has the side effect of making sleep more accurate.
func wasteCPU() chan struct{} {
done := make(chan struct{})
go func() {
for {
select {
case <-done:
return
default:
}
}
}()
// pause for a short amount of time to allow the
// power management to recognise load has risen.
<-time.After(300 * time.Millisecond)
return done
}
func testParallelSleep(t *testing.T) {
defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
defer close(wasteCPU())
sleepSec := 1
if runtime.GOARCH == "arm" {
// on ARM, the 1.3s deadline is frequently missed,
// so increase sleep time to 2s
sleepSec = 2
}
start := time.Now()
parallelSleep(sleepSec)
dt := time.Now().Sub(start)
dt := time.Since(start)
t.Logf("sleep(%d) slept for %v", sleepSec, dt)
// bug used to run sleeps in serial, producing a 2*sleepSec-second delay.
if dt >= time.Duration(sleepSec)*1300*time.Millisecond {
t.Fatalf("parallel %d-second sleeps slept for %f seconds", sleepSec, dt.Seconds())
......
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