X try to use double-buffereing and queue read syscall into /dev/fuse while we are handling request

It still does not help and so hanwen/go-fuse remains the best Go fuse
library from performance point of view

a3a68a84

fuseutil/file_system.go

@@ -101,8 +101,9 @@ func (s *fileSystemServer) ServeOps(c *fuse.Connection) {
 		s.fs.Destroy()
 	}()
 
-	s.serveInFlight.Add(1)
-	s.serveOps(c)
+	s.serveInFlight.Add(4)
+	go s.serveOps(c)
+	go s.serveOps(c)
 }
 
 func (s *fileSystemServer) serveOps(c *fuse.Connection) {
@@ -123,6 +124,8 @@ func (s *fileSystemServer) serveOps(c *fuse.Connection) {
 	// queue. see e.g. https://github.com/golang/go/issues/15110 for details.
 	//
 	// improving FUSE request-response latency also improves IO throughput.
+	//
+	// XXX it does not improve throughput for jacobsa/fuse.
 	s.serveInFlight.Add(1)
 	go s.serveOps(c)