qemu: iothreads: Add iothread support for scsi

Add a hypervisor configuration to specify if IO should
be handled in a separate thread. Add support for iothreads for
virtio-scsi for now. Since we attach all scsi drives to the
same scsi controller, all the drives will be handled in a separate
IO thread which would still give better performance.

Going forward we need to assess if adding more controllers and
attaching iothreasds to each of them with distributing drives
among teh scsi controllers should be done, based on more performance
analysis.

Signed-off-by: Archana Shinde <archana.m.shinde@intel.com>

virtcontainers/hypervisor.go

@@ -201,6 +201,10 @@ type HypervisorConfig struct {
 	// DisableBlockDeviceUse disallows a block device from being used.
 	DisableBlockDeviceUse bool
 
+	// EnableIOThreads enables IO to be processed in a separate thread.
+	// Supported currently for virtio-scsi driver.
+	EnableIOThreads bool
+
 	// Debug changes the default hypervisor and kernel parameters to
 	// enable debug output where available.
 	Debug bool

virtcontainers/qemu.go

@@ -379,8 +379,9 @@ func (q *qemu) createPod(podConfig PodConfig) error {
 		return err
 	}
 
+	var ioThread *govmmQemu.IOThread
 	if q.config.BlockDeviceDriver == VirtioSCSI {
-		devices = q.arch.appendSCSIController(devices)
+		devices, ioThread = q.arch.appendSCSIController(devices, q.config.EnableIOThreads)
 	}
 
 	cpuModel := q.arch.cpuModel()
@@ -414,6 +415,10 @@ func (q *qemu) createPod(podConfig PodConfig) error {
 		Bios:        firmwarePath,
 	}
 
+	if ioThread != nil {
+		qemuConfig.IOThreads = []govmmQemu.IOThread{*ioThread}
+	}
+
 	q.qemuConfig = qemuConfig
 
 	return nil

virtcontainers/qemu_arch_base.go

@@ -66,7 +66,7 @@ type qemuArch interface {
 	appendImage(devices []govmmQemu.Device, path string) ([]govmmQemu.Device, error)
 
 	// appendSCSIController appens a SCSI controller to devices
-	appendSCSIController(devices []govmmQemu.Device) []govmmQemu.Device
+	appendSCSIController(devices []govmmQemu.Device, enableIOThreads bool) ([]govmmQemu.Device, *govmmQemu.IOThread)
 
 	// appendBridges appends bridges to devices
 	appendBridges(devices []govmmQemu.Device, bridges []Bridge) []govmmQemu.Device
@@ -300,15 +300,27 @@ func (q *qemuArchBase) appendImage(devices []govmmQemu.Device, path string) ([]g
 	return q.appendBlockDevice(devices, drive), nil
 }
 
-func (q *qemuArchBase) appendSCSIController(devices []govmmQemu.Device) []govmmQemu.Device {
+func (q *qemuArchBase) appendSCSIController(devices []govmmQemu.Device, enableIOThreads bool) ([]govmmQemu.Device, *govmmQemu.IOThread) {
 	scsiController := govmmQemu.SCSIController{
 		ID:            scsiControllerID,
 		DisableModern: q.nestedRun,
 	}
 
+	var t *govmmQemu.IOThread
+
+	if enableIOThreads {
+		randBytes, _ := generateRandomBytes(8)
+
+		t = &govmmQemu.IOThread{
+			ID: fmt.Sprintf("%s-%s", "iothread", hex.EncodeToString(randBytes)),
+		}
+
+		scsiController.IOThread = t.ID
+	}
+
 	devices = append(devices, scsiController)
 
-	return devices
+	return devices, t
 }
 
 // appendBridges appends to devices the given bridges

virtcontainers/qemu_arch_base_test.go

@@ -470,6 +470,10 @@ func TestQemuArchBaseAppendSCSIController(t *testing.T) {
 		},
 	}
 
-	devices = qemuArchBase.appendSCSIController(devices)
+	devices, ioThread := qemuArchBase.appendSCSIController(devices, false)
 	assert.Equal(expectedOut, devices)
+	assert.Nil(ioThread)
+
+	_, ioThread = qemuArchBase.appendSCSIController(devices, true)
+	assert.NotNil(ioThread)
 }