Merge pull request #6933 from mvo5/min-gomaxprocs-2

cmd/snapd: ensure GOMAXPROCS is at least 2

1 files changed, 19 insertions, 0 deletions

diff --git a/cmd/snapd/main.go b/cmd/snapd/main.go
index aafabbfe98..6940cf06a4 100644
--- a/cmd/snapd/main.go
+++ b/cmd/snapd/main.go
@@ -23,6 +23,7 @@ import (
	"fmt"
	"os"
	"os/signal"
+	"runtime"
	"syscall"
	"time"
 
@@ -53,6 +54,24 @@ func init() {
 func main() {
	cmd.ExecInSnapdOrCoreSnap()
 
+	// The Go scheduler by default has a single operating system
+	// thread per processor core, and does its own goroutine
+	// scheduling inside of that thread. For I/O operations that
+	// the Go runtime knows about, it has mechanisms to reschedule
+	// goroutines so the system thread isn't blocked waiting for
+	// I/O. If a goroutine performs a blocking system call which
+	// the go runtime doesn't have special optimizations for, the
+	// system thread can become blocked waiting for the syscall.
+	// This can dramatically reduce runtime performance, and the
+	// problem is much worse on single processor systems because
+	// there is normally only a single system thread.
+	//
+	// We workaround by increasing the number of procs to a
+	// minimum of two.
+	if runtime.GOMAXPROCS(-1) == 1 {
+	runtime.GOMAXPROCS(2)
+	}
+
	ch := make(chan os.Signal, 2)
	signal.Notify(ch, syscall.SIGINT, syscall.SIGTERM)
	if err := run(ch); err != nil {