diff options
author | Andrei Vagin <avagin@google.com> | 2019-03-29 10:43:31 -0700 |
---|---|---|
committer | Dmitry Vyukov <dvyukov@google.com> | 2019-04-09 07:45:26 +0000 |
commit | 4166ff42c09cae4ca9e15154627e7cfc80586c65 (patch) | |
tree | 135a22462d208dc313e3dd18369ae457362a6786 /src/runtime/proc_test.go | |
parent | 08e1823a632783e3f71b358f2f546ab0f13a6d98 (diff) | |
download | go-4166ff42c09cae4ca9e15154627e7cfc80586c65.tar.gz go-4166ff42c09cae4ca9e15154627e7cfc80586c65.zip |
runtime: preempt a goroutine which calls a lot of short system calls
A goroutine should be preempted if it runs for 10ms without blocking.
We found that this doesn't work for goroutines which call short system calls.
For example, the next program can stuck for seconds without this fix:
$ cat main.go
package main
import (
"runtime"
"syscall"
)
func main() {
runtime.GOMAXPROCS(1)
c := make(chan int)
go func() {
c <- 1
for {
t := syscall.Timespec{
Nsec: 300,
}
if true {
syscall.Nanosleep(&t, nil)
}
}
}()
<-c
}
$ time go run main.go
real 0m8.796s
user 0m0.367s
sys 0m0.893s
Updates #10958
Change-Id: Id3be54d3779cc28bfc8b33fe578f13778f1ae2a2
Reviewed-on: https://go-review.googlesource.com/c/go/+/170138
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Run-TryBot: Dmitry Vyukov <dvyukov@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Diffstat (limited to 'src/runtime/proc_test.go')
-rw-r--r-- | src/runtime/proc_test.go | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/src/runtime/proc_test.go b/src/runtime/proc_test.go index 1715324aa0..09b0652bee 100644 --- a/src/runtime/proc_test.go +++ b/src/runtime/proc_test.go @@ -5,6 +5,7 @@ package runtime_test import ( + "fmt" "math" "net" "runtime" @@ -910,3 +911,69 @@ func TestLockOSThreadAvoidsStatePropagation(t *testing.T) { t.Errorf("want %q, got %q", want, output) } } + +// fakeSyscall emulates a system call. +//go:nosplit +func fakeSyscall(duration time.Duration) { + runtime.Entersyscall() + for start := runtime.Nanotime(); runtime.Nanotime()-start < int64(duration); { + } + runtime.Exitsyscall() +} + +// Check that a goroutine will be preempted if it is calling short system calls. +func testPreemptionAfterSyscall(t *testing.T, syscallDuration time.Duration) { + if runtime.GOARCH == "wasm" { + t.Skip("no preemption on wasm yet") + } + + defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2)) + + interations := 10 + if testing.Short() { + interations = 1 + } + const ( + maxDuration = 3 * time.Second + nroutines = 8 + ) + + for i := 0; i < interations; i++ { + c := make(chan bool, nroutines) + stop := uint32(0) + + start := time.Now() + for g := 0; g < nroutines; g++ { + go func(stop *uint32) { + c <- true + for atomic.LoadUint32(stop) == 0 { + fakeSyscall(syscallDuration) + } + c <- true + }(&stop) + } + // wait until all goroutines have started. + for g := 0; g < nroutines; g++ { + <-c + } + atomic.StoreUint32(&stop, 1) + // wait until all goroutines have finished. + for g := 0; g < nroutines; g++ { + <-c + } + duration := time.Since(start) + + if duration > maxDuration { + t.Errorf("timeout exceeded: %v (%v)", duration, maxDuration) + } + } +} + +func TestPreemptionAfterSyscall(t *testing.T) { + for _, i := range []time.Duration{10, 100, 1000} { + d := i * time.Microsecond + t.Run(fmt.Sprint(d), func(t *testing.T) { + testPreemptionAfterSyscall(t, d) + }) + } +} |