[v4] virtio-pci: enable blk and scsi multi-queue by default

[PATCH v4 2/5] virtio-scsi: introduce a constant for fixed virtqueues

Posted by Stefan Hajnoczi 5 years, 5 months ago

The event and control virtqueues are always present, regardless of the
multi-queue configuration.  Define a constant so that virtqueue number
calculations are easier to read.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
---
 include/hw/virtio/virtio-scsi.h | 3 +++
 hw/scsi/vhost-user-scsi.c       | 2 +-
 hw/scsi/virtio-scsi.c           | 7 ++++---
 hw/virtio/vhost-scsi-pci.c      | 3 ++-
 hw/virtio/vhost-user-scsi-pci.c | 3 ++-
 hw/virtio/virtio-scsi-pci.c     | 3 ++-
 6 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
index 24e768909d..9f293bcb80 100644
--- a/include/hw/virtio/virtio-scsi.h
+++ b/include/hw/virtio/virtio-scsi.h
@@ -36,6 +36,9 @@
 #define VIRTIO_SCSI_MAX_TARGET  255
 #define VIRTIO_SCSI_MAX_LUN     16383
 
+/* Number of virtqueues that are always present */
+#define VIRTIO_SCSI_VQ_NUM_FIXED    2
+
 typedef struct virtio_scsi_cmd_req VirtIOSCSICmdReq;
 typedef struct virtio_scsi_cmd_resp VirtIOSCSICmdResp;
 typedef struct virtio_scsi_ctrl_tmf_req VirtIOSCSICtrlTMFReq;
diff --git a/hw/scsi/vhost-user-scsi.c b/hw/scsi/vhost-user-scsi.c
index cbb5d97599..f8bd158c31 100644
--- a/hw/scsi/vhost-user-scsi.c
+++ b/hw/scsi/vhost-user-scsi.c
@@ -115,7 +115,7 @@ static void vhost_user_scsi_realize(DeviceState *dev, Error **errp)
         goto free_virtio;
     }
 
-    vsc->dev.nvqs = 2 + vs->conf.num_queues;
+    vsc->dev.nvqs = VIRTIO_SCSI_VQ_NUM_FIXED + vs->conf.num_queues;
     vsc->dev.vqs = g_new0(struct vhost_virtqueue, vsc->dev.nvqs);
     vsc->dev.vq_index = 0;
     vsc->dev.backend_features = 0;
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 9b72094a61..f3d60683bd 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -191,7 +191,7 @@ static void virtio_scsi_save_request(QEMUFile *f, SCSIRequest *sreq)
     VirtIOSCSIReq *req = sreq->hba_private;
     VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(req->dev);
     VirtIODevice *vdev = VIRTIO_DEVICE(req->dev);
-    uint32_t n = virtio_get_queue_index(req->vq) - 2;
+    uint32_t n = virtio_get_queue_index(req->vq) - VIRTIO_SCSI_VQ_NUM_FIXED;
 
     assert(n < vs->conf.num_queues);
     qemu_put_be32s(f, &n);
@@ -892,10 +892,11 @@ void virtio_scsi_common_realize(DeviceState *dev,
                 sizeof(VirtIOSCSIConfig));
 
     if (s->conf.num_queues == 0 ||
-            s->conf.num_queues > VIRTIO_QUEUE_MAX - 2) {
+            s->conf.num_queues > VIRTIO_QUEUE_MAX - VIRTIO_SCSI_VQ_NUM_FIXED) {
         error_setg(errp, "Invalid number of queues (= %" PRIu32 "), "
                          "must be a positive integer less than %d.",
-                   s->conf.num_queues, VIRTIO_QUEUE_MAX - 2);
+                   s->conf.num_queues,
+                   VIRTIO_QUEUE_MAX - VIRTIO_SCSI_VQ_NUM_FIXED);
         virtio_cleanup(vdev);
         return;
     }
diff --git a/hw/virtio/vhost-scsi-pci.c b/hw/virtio/vhost-scsi-pci.c
index 5da6bb6449..2b25db9a3c 100644
--- a/hw/virtio/vhost-scsi-pci.c
+++ b/hw/virtio/vhost-scsi-pci.c
@@ -50,7 +50,8 @@ static void vhost_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
     VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev);
 
     if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
-        vpci_dev->nvectors = vs->conf.num_queues + 3;
+        vpci_dev->nvectors = vs->conf.num_queues +
+                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
     }
 
     qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
diff --git a/hw/virtio/vhost-user-scsi-pci.c b/hw/virtio/vhost-user-scsi-pci.c
index 6f3375fe55..80710ab170 100644
--- a/hw/virtio/vhost-user-scsi-pci.c
+++ b/hw/virtio/vhost-user-scsi-pci.c
@@ -56,7 +56,8 @@ static void vhost_user_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
     VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev);
 
     if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
-        vpci_dev->nvectors = vs->conf.num_queues + 3;
+        vpci_dev->nvectors = vs->conf.num_queues +
+                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
     }
 
     qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
diff --git a/hw/virtio/virtio-scsi-pci.c b/hw/virtio/virtio-scsi-pci.c
index e82e7e5680..c52d68053a 100644
--- a/hw/virtio/virtio-scsi-pci.c
+++ b/hw/virtio/virtio-scsi-pci.c
@@ -51,7 +51,8 @@ static void virtio_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
     char *bus_name;
 
     if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
-        vpci_dev->nvectors = vs->conf.num_queues + 3;
+        vpci_dev->nvectors = vs->conf.num_queues +
+                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
     }
 
     /*
-- 
2.25.4

Re: [PATCH v4 2/5] virtio-scsi: introduce a constant for fixed virtqueues

Posted by Pankaj Gupta 5 years, 5 months ago

> The event and control virtqueues are always present, regardless of the
> multi-queue configuration.  Define a constant so that virtqueue number
> calculations are easier to read.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> ---
>  include/hw/virtio/virtio-scsi.h | 3 +++
>  hw/scsi/vhost-user-scsi.c       | 2 +-
>  hw/scsi/virtio-scsi.c           | 7 ++++---
>  hw/virtio/vhost-scsi-pci.c      | 3 ++-
>  hw/virtio/vhost-user-scsi-pci.c | 3 ++-
>  hw/virtio/virtio-scsi-pci.c     | 3 ++-
>  6 files changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
> index 24e768909d..9f293bcb80 100644
> --- a/include/hw/virtio/virtio-scsi.h
> +++ b/include/hw/virtio/virtio-scsi.h
> @@ -36,6 +36,9 @@
>  #define VIRTIO_SCSI_MAX_TARGET  255
>  #define VIRTIO_SCSI_MAX_LUN     16383
>
> +/* Number of virtqueues that are always present */
> +#define VIRTIO_SCSI_VQ_NUM_FIXED    2
> +
>  typedef struct virtio_scsi_cmd_req VirtIOSCSICmdReq;
>  typedef struct virtio_scsi_cmd_resp VirtIOSCSICmdResp;
>  typedef struct virtio_scsi_ctrl_tmf_req VirtIOSCSICtrlTMFReq;
> diff --git a/hw/scsi/vhost-user-scsi.c b/hw/scsi/vhost-user-scsi.c
> index cbb5d97599..f8bd158c31 100644
> --- a/hw/scsi/vhost-user-scsi.c
> +++ b/hw/scsi/vhost-user-scsi.c
> @@ -115,7 +115,7 @@ static void vhost_user_scsi_realize(DeviceState *dev, Error **errp)
>          goto free_virtio;
>      }
>
> -    vsc->dev.nvqs = 2 + vs->conf.num_queues;
> +    vsc->dev.nvqs = VIRTIO_SCSI_VQ_NUM_FIXED + vs->conf.num_queues;
>      vsc->dev.vqs = g_new0(struct vhost_virtqueue, vsc->dev.nvqs);
>      vsc->dev.vq_index = 0;
>      vsc->dev.backend_features = 0;
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index 9b72094a61..f3d60683bd 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -191,7 +191,7 @@ static void virtio_scsi_save_request(QEMUFile *f, SCSIRequest *sreq)
>      VirtIOSCSIReq *req = sreq->hba_private;
>      VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(req->dev);
>      VirtIODevice *vdev = VIRTIO_DEVICE(req->dev);
> -    uint32_t n = virtio_get_queue_index(req->vq) - 2;
> +    uint32_t n = virtio_get_queue_index(req->vq) - VIRTIO_SCSI_VQ_NUM_FIXED;
>
>      assert(n < vs->conf.num_queues);
>      qemu_put_be32s(f, &n);
> @@ -892,10 +892,11 @@ void virtio_scsi_common_realize(DeviceState *dev,
>                  sizeof(VirtIOSCSIConfig));
>
>      if (s->conf.num_queues == 0 ||
> -            s->conf.num_queues > VIRTIO_QUEUE_MAX - 2) {
> +            s->conf.num_queues > VIRTIO_QUEUE_MAX - VIRTIO_SCSI_VQ_NUM_FIXED) {
>          error_setg(errp, "Invalid number of queues (= %" PRIu32 "), "
>                           "must be a positive integer less than %d.",
> -                   s->conf.num_queues, VIRTIO_QUEUE_MAX - 2);
> +                   s->conf.num_queues,
> +                   VIRTIO_QUEUE_MAX - VIRTIO_SCSI_VQ_NUM_FIXED);
>          virtio_cleanup(vdev);
>          return;
>      }
> diff --git a/hw/virtio/vhost-scsi-pci.c b/hw/virtio/vhost-scsi-pci.c
> index 5da6bb6449..2b25db9a3c 100644
> --- a/hw/virtio/vhost-scsi-pci.c
> +++ b/hw/virtio/vhost-scsi-pci.c
> @@ -50,7 +50,8 @@ static void vhost_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>      VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev);
>
>      if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
> -        vpci_dev->nvectors = vs->conf.num_queues + 3;
> +        vpci_dev->nvectors = vs->conf.num_queues +
> +                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
>      }
>
>      qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
> diff --git a/hw/virtio/vhost-user-scsi-pci.c b/hw/virtio/vhost-user-scsi-pci.c
> index 6f3375fe55..80710ab170 100644
> --- a/hw/virtio/vhost-user-scsi-pci.c
> +++ b/hw/virtio/vhost-user-scsi-pci.c
> @@ -56,7 +56,8 @@ static void vhost_user_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>      VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev);
>
>      if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
> -        vpci_dev->nvectors = vs->conf.num_queues + 3;
> +        vpci_dev->nvectors = vs->conf.num_queues +
> +                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
>      }
>
>      qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
> diff --git a/hw/virtio/virtio-scsi-pci.c b/hw/virtio/virtio-scsi-pci.c
> index e82e7e5680..c52d68053a 100644
> --- a/hw/virtio/virtio-scsi-pci.c
> +++ b/hw/virtio/virtio-scsi-pci.c
> @@ -51,7 +51,8 @@ static void virtio_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>      char *bus_name;
>
>      if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
> -        vpci_dev->nvectors = vs->conf.num_queues + 3;
> +        vpci_dev->nvectors = vs->conf.num_queues +
> +                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
>      }
>
>      /*
> --
Better readability with no change in logic. Code looks good to me.

Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>

Re: [PATCH v4 2/5] virtio-scsi: introduce a constant for fixed virtqueues

Posted by Raphael Norwitz 5 years, 5 months ago

On Wed, May 27, 2020 at 6:32 AM Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> The event and control virtqueues are always present, regardless of the
> multi-queue configuration.  Define a constant so that virtqueue number
> calculations are easier to read.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> ---
>  include/hw/virtio/virtio-scsi.h | 3 +++
>  hw/scsi/vhost-user-scsi.c       | 2 +-
>  hw/scsi/virtio-scsi.c           | 7 ++++---
>  hw/virtio/vhost-scsi-pci.c      | 3 ++-
>  hw/virtio/vhost-user-scsi-pci.c | 3 ++-
>  hw/virtio/virtio-scsi-pci.c     | 3 ++-
>  6 files changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
> index 24e768909d..9f293bcb80 100644
> --- a/include/hw/virtio/virtio-scsi.h
> +++ b/include/hw/virtio/virtio-scsi.h
> @@ -36,6 +36,9 @@
>  #define VIRTIO_SCSI_MAX_TARGET  255
>  #define VIRTIO_SCSI_MAX_LUN     16383
>
> +/* Number of virtqueues that are always present */
> +#define VIRTIO_SCSI_VQ_NUM_FIXED    2
> +
>  typedef struct virtio_scsi_cmd_req VirtIOSCSICmdReq;
>  typedef struct virtio_scsi_cmd_resp VirtIOSCSICmdResp;
>  typedef struct virtio_scsi_ctrl_tmf_req VirtIOSCSICtrlTMFReq;
> diff --git a/hw/scsi/vhost-user-scsi.c b/hw/scsi/vhost-user-scsi.c
> index cbb5d97599..f8bd158c31 100644
> --- a/hw/scsi/vhost-user-scsi.c
> +++ b/hw/scsi/vhost-user-scsi.c
> @@ -115,7 +115,7 @@ static void vhost_user_scsi_realize(DeviceState *dev, Error **errp)
>          goto free_virtio;
>      }
>
> -    vsc->dev.nvqs = 2 + vs->conf.num_queues;
> +    vsc->dev.nvqs = VIRTIO_SCSI_VQ_NUM_FIXED + vs->conf.num_queues;
>      vsc->dev.vqs = g_new0(struct vhost_virtqueue, vsc->dev.nvqs);
>      vsc->dev.vq_index = 0;
>      vsc->dev.backend_features = 0;
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index 9b72094a61..f3d60683bd 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -191,7 +191,7 @@ static void virtio_scsi_save_request(QEMUFile *f, SCSIRequest *sreq)
>      VirtIOSCSIReq *req = sreq->hba_private;
>      VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(req->dev);
>      VirtIODevice *vdev = VIRTIO_DEVICE(req->dev);
> -    uint32_t n = virtio_get_queue_index(req->vq) - 2;
> +    uint32_t n = virtio_get_queue_index(req->vq) - VIRTIO_SCSI_VQ_NUM_FIXED;
>
>      assert(n < vs->conf.num_queues);
>      qemu_put_be32s(f, &n);
> @@ -892,10 +892,11 @@ void virtio_scsi_common_realize(DeviceState *dev,
>                  sizeof(VirtIOSCSIConfig));
>
>      if (s->conf.num_queues == 0 ||
> -            s->conf.num_queues > VIRTIO_QUEUE_MAX - 2) {
> +            s->conf.num_queues > VIRTIO_QUEUE_MAX - VIRTIO_SCSI_VQ_NUM_FIXED) {
>          error_setg(errp, "Invalid number of queues (= %" PRIu32 "), "
>                           "must be a positive integer less than %d.",
> -                   s->conf.num_queues, VIRTIO_QUEUE_MAX - 2);
> +                   s->conf.num_queues,
> +                   VIRTIO_QUEUE_MAX - VIRTIO_SCSI_VQ_NUM_FIXED);
>          virtio_cleanup(vdev);
>          return;
>      }
> diff --git a/hw/virtio/vhost-scsi-pci.c b/hw/virtio/vhost-scsi-pci.c
> index 5da6bb6449..2b25db9a3c 100644
> --- a/hw/virtio/vhost-scsi-pci.c
> +++ b/hw/virtio/vhost-scsi-pci.c
> @@ -50,7 +50,8 @@ static void vhost_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>      VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev);
>
>      if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
> -        vpci_dev->nvectors = vs->conf.num_queues + 3;
> +        vpci_dev->nvectors = vs->conf.num_queues +
> +                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
>      }
>
>      qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
> diff --git a/hw/virtio/vhost-user-scsi-pci.c b/hw/virtio/vhost-user-scsi-pci.c
> index 6f3375fe55..80710ab170 100644
> --- a/hw/virtio/vhost-user-scsi-pci.c
> +++ b/hw/virtio/vhost-user-scsi-pci.c
> @@ -56,7 +56,8 @@ static void vhost_user_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>      VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev);
>
>      if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
> -        vpci_dev->nvectors = vs->conf.num_queues + 3;
> +        vpci_dev->nvectors = vs->conf.num_queues +
> +                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
>      }
>
>      qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
> diff --git a/hw/virtio/virtio-scsi-pci.c b/hw/virtio/virtio-scsi-pci.c
> index e82e7e5680..c52d68053a 100644
> --- a/hw/virtio/virtio-scsi-pci.c
> +++ b/hw/virtio/virtio-scsi-pci.c
> @@ -51,7 +51,8 @@ static void virtio_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>      char *bus_name;
>
>      if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
> -        vpci_dev->nvectors = vs->conf.num_queues + 3;
> +        vpci_dev->nvectors = vs->conf.num_queues +
> +                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
>      }
>
>      /*
> --
> 2.25.4
>

Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>

Re: [PATCH v4 2/5] virtio-scsi: introduce a constant for fixed virtqueues

Posted by Philippe Mathieu-Daudé 5 years, 5 months ago

On 5/27/20 12:29 PM, Stefan Hajnoczi wrote:
> The event and control virtqueues are always present, regardless of the
> multi-queue configuration.  Define a constant so that virtqueue number
> calculations are easier to read.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> ---
>  include/hw/virtio/virtio-scsi.h | 3 +++
>  hw/scsi/vhost-user-scsi.c       | 2 +-
>  hw/scsi/virtio-scsi.c           | 7 ++++---
>  hw/virtio/vhost-scsi-pci.c      | 3 ++-
>  hw/virtio/vhost-user-scsi-pci.c | 3 ++-
>  hw/virtio/virtio-scsi-pci.c     | 3 ++-
>  6 files changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
> index 24e768909d..9f293bcb80 100644
> --- a/include/hw/virtio/virtio-scsi.h
> +++ b/include/hw/virtio/virtio-scsi.h
> @@ -36,6 +36,9 @@
>  #define VIRTIO_SCSI_MAX_TARGET  255
>  #define VIRTIO_SCSI_MAX_LUN     16383
>  
> +/* Number of virtqueues that are always present */
> +#define VIRTIO_SCSI_VQ_NUM_FIXED    2
> +
>  typedef struct virtio_scsi_cmd_req VirtIOSCSICmdReq;
>  typedef struct virtio_scsi_cmd_resp VirtIOSCSICmdResp;
>  typedef struct virtio_scsi_ctrl_tmf_req VirtIOSCSICtrlTMFReq;
> diff --git a/hw/scsi/vhost-user-scsi.c b/hw/scsi/vhost-user-scsi.c
> index cbb5d97599..f8bd158c31 100644
> --- a/hw/scsi/vhost-user-scsi.c
> +++ b/hw/scsi/vhost-user-scsi.c
> @@ -115,7 +115,7 @@ static void vhost_user_scsi_realize(DeviceState *dev, Error **errp)
>          goto free_virtio;
>      }
>  
> -    vsc->dev.nvqs = 2 + vs->conf.num_queues;
> +    vsc->dev.nvqs = VIRTIO_SCSI_VQ_NUM_FIXED + vs->conf.num_queues;
>      vsc->dev.vqs = g_new0(struct vhost_virtqueue, vsc->dev.nvqs);
>      vsc->dev.vq_index = 0;
>      vsc->dev.backend_features = 0;
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index 9b72094a61..f3d60683bd 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -191,7 +191,7 @@ static void virtio_scsi_save_request(QEMUFile *f, SCSIRequest *sreq)
>      VirtIOSCSIReq *req = sreq->hba_private;
>      VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(req->dev);
>      VirtIODevice *vdev = VIRTIO_DEVICE(req->dev);
> -    uint32_t n = virtio_get_queue_index(req->vq) - 2;
> +    uint32_t n = virtio_get_queue_index(req->vq) - VIRTIO_SCSI_VQ_NUM_FIXED;
>  
>      assert(n < vs->conf.num_queues);
>      qemu_put_be32s(f, &n);
> @@ -892,10 +892,11 @@ void virtio_scsi_common_realize(DeviceState *dev,
>                  sizeof(VirtIOSCSIConfig));
>  
>      if (s->conf.num_queues == 0 ||
> -            s->conf.num_queues > VIRTIO_QUEUE_MAX - 2) {
> +            s->conf.num_queues > VIRTIO_QUEUE_MAX - VIRTIO_SCSI_VQ_NUM_FIXED) {
>          error_setg(errp, "Invalid number of queues (= %" PRIu32 "), "
>                           "must be a positive integer less than %d.",
> -                   s->conf.num_queues, VIRTIO_QUEUE_MAX - 2);
> +                   s->conf.num_queues,
> +                   VIRTIO_QUEUE_MAX - VIRTIO_SCSI_VQ_NUM_FIXED);
>          virtio_cleanup(vdev);
>          return;
>      }
> diff --git a/hw/virtio/vhost-scsi-pci.c b/hw/virtio/vhost-scsi-pci.c
> index 5da6bb6449..2b25db9a3c 100644
> --- a/hw/virtio/vhost-scsi-pci.c
> +++ b/hw/virtio/vhost-scsi-pci.c
> @@ -50,7 +50,8 @@ static void vhost_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>      VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev);
>  
>      if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
> -        vpci_dev->nvectors = vs->conf.num_queues + 3;
> +        vpci_dev->nvectors = vs->conf.num_queues +
> +                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
>      }
>  
>      qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
> diff --git a/hw/virtio/vhost-user-scsi-pci.c b/hw/virtio/vhost-user-scsi-pci.c
> index 6f3375fe55..80710ab170 100644
> --- a/hw/virtio/vhost-user-scsi-pci.c
> +++ b/hw/virtio/vhost-user-scsi-pci.c
> @@ -56,7 +56,8 @@ static void vhost_user_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>      VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev);
>  
>      if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
> -        vpci_dev->nvectors = vs->conf.num_queues + 3;
> +        vpci_dev->nvectors = vs->conf.num_queues +
> +                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
>      }
>  
>      qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
> diff --git a/hw/virtio/virtio-scsi-pci.c b/hw/virtio/virtio-scsi-pci.c
> index e82e7e5680..c52d68053a 100644
> --- a/hw/virtio/virtio-scsi-pci.c
> +++ b/hw/virtio/virtio-scsi-pci.c
> @@ -51,7 +51,8 @@ static void virtio_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>      char *bus_name;
>  
>      if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
> -        vpci_dev->nvectors = vs->conf.num_queues + 3;
> +        vpci_dev->nvectors = vs->conf.num_queues +
> +                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
>      }
>  
>      /*
> 

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

[PATCH v4 1/5] virtio-pci: add virtio_pci_optimal_num_queues() helper
[PATCH v4 2/5] virtio-scsi: introduce a constant for fixed virtqueues
[PATCH v4 3/5] virtio-scsi: default num_queues to -smp N
[PATCH v4 4/5] virtio-blk: default num_queues to -smp N
[PATCH v4 5/5] vhost-user-blk: default num_queues to -smp N