[PATCH 5/5] vhost-user-blk: default num_queues to -smp N

[Stefan Hajnoczi <stefanha@redhat.com>]

Automatically size the number of request virtqueues to match the number
of vCPUs.  This ensures that completion interrupts are handled on the
same vCPU that submitted the request.  No IPI is necessary to complete
an I/O request and performance is improved.

This patch duplicates the .get_num_virtqueues() function because
vhost-user-blk defines its own qdev property fields and does not share
VirtIOBlkConf.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/block/vhost-user-blk.c          | 15 +++++++++++++++
 hw/core/machine.c                  |  1 +
 hw/virtio/vhost-user-blk-pci.c     |  3 ++-
 include/hw/virtio/vhost-user-blk.h |  1 +
 4 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
index 98b383f90e..ac61ce9835 100644
--- a/hw/block/vhost-user-blk.c
+++ b/hw/block/vhost-user-blk.c
@@ -21,6 +21,7 @@
 #include "qemu/error-report.h"
 #include "qemu/cutils.h"
 #include "qom/object.h"
+#include "hw/boards.h"
 #include "hw/qdev-core.h"
 #include "hw/qdev-properties.h"
 #include "hw/virtio/vhost.h"
@@ -391,6 +392,17 @@ static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
     }
 }
 
+static uint32_t vhost_user_blk_get_num_virtqueues(VirtIODevice *vdev)
+{
+    VHostUserBlk *s = VHOST_USER_BLK(vdev);
+
+    if (s->num_queues == 1 && s->auto_num_queues) {
+        return current_machine->smp.cpus;
+    }
+
+    return s->num_queues;
+}
+
 static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
@@ -403,6 +415,7 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
         return;
     }
 
+    s->num_queues = vhost_user_blk_get_num_virtqueues(vdev);
     if (!s->num_queues || s->num_queues > VIRTIO_QUEUE_MAX) {
         error_setg(errp, "vhost-user-blk: invalid number of IO queues");
         return;
@@ -501,6 +514,7 @@ static const VMStateDescription vmstate_vhost_user_blk = {
 static Property vhost_user_blk_properties[] = {
     DEFINE_PROP_CHR("chardev", VHostUserBlk, chardev),
     DEFINE_PROP_UINT16("num-queues", VHostUserBlk, num_queues, 1),
+    DEFINE_PROP_BOOL("auto-num-queues", VHostUserBlk, auto_num_queues, true),
     DEFINE_PROP_UINT32("queue-size", VHostUserBlk, queue_size, 128),
     DEFINE_PROP_BIT("config-wce", VHostUserBlk, config_wce, 0, true),
     DEFINE_PROP_END_OF_LIST(),
@@ -514,6 +528,7 @@ static void vhost_user_blk_class_init(ObjectClass *klass, void *data)
     dc->props = vhost_user_blk_properties;
     dc->vmsd = &vmstate_vhost_user_blk;
     set_bit(DEVICE_CATEGORY_STORAGE, dc->categories);
+    vdc->get_num_virtqueues = vhost_user_blk_get_num_virtqueues;
     vdc->realize = vhost_user_blk_device_realize;
     vdc->unrealize = vhost_user_blk_device_unrealize;
     vdc->get_config = vhost_user_blk_update_config;
diff --git a/hw/core/machine.c b/hw/core/machine.c
index a33d1e93b1..0d4142c3c8 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -35,6 +35,7 @@ GlobalProperty hw_compat_4_2[] = {
     { "virtio-scsi-device", "seg_max_adjust", "off"},
     { "vhost-blk-device", "seg_max_adjust", "off"},
     { "vhost-scsi", "auto_num_queues", "off"},
+    { "vhost-user-blk", "auto-num-queues", "off"},
     { "vhost-user-scsi", "auto_num_queues", "off"},
     { "usb-host", "suppress-remote-wake", "off" },
     { "usb-redir", "suppress-remote-wake", "off" },
diff --git a/hw/virtio/vhost-user-blk-pci.c b/hw/virtio/vhost-user-blk-pci.c
index 1dc834a3ff..328c6a4066 100644
--- a/hw/virtio/vhost-user-blk-pci.c
+++ b/hw/virtio/vhost-user-blk-pci.c
@@ -53,9 +53,10 @@ static void vhost_user_blk_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
 {
     VHostUserBlkPCI *dev = VHOST_USER_BLK_PCI(vpci_dev);
     DeviceState *vdev = DEVICE(&dev->vdev);
+    VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(vdev);
 
     if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
-        vpci_dev->nvectors = dev->vdev.num_queues + 1;
+        vpci_dev->nvectors = vdc->get_num_virtqueues(VIRTIO_DEVICE(vdev)) + 1;
     }
 
     qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
diff --git a/include/hw/virtio/vhost-user-blk.h b/include/hw/virtio/vhost-user-blk.h
index 108bfadeeb..09d1fdf722 100644
--- a/include/hw/virtio/vhost-user-blk.h
+++ b/include/hw/virtio/vhost-user-blk.h
@@ -31,6 +31,7 @@ typedef struct VHostUserBlk {
     int32_t bootindex;
     struct virtio_blk_config blkcfg;
     uint16_t num_queues;
+    bool auto_num_queues;
     uint32_t queue_size;
     uint32_t config_wce;
     struct vhost_dev dev;
-- 
2.24.1