diff mbox series

[v1,1/4] virtio: introduce VIRTQUEUE_DEFUALT_SIZE instead of hardcoded constants

Message ID 20200129140702.5411-2-dplotnikov@virtuozzo.com
State New
Headers show
Series Increase default virtqueue size to improve performance | expand

Commit Message

Denis Plotnikov Jan. 29, 2020, 2:06 p.m. UTC 
Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
---
 hw/block/virtio-blk.c      | 6 ++++--
 hw/scsi/virtio-scsi.c      | 5 +++--
 include/hw/virtio/virtio.h | 1 +
 3 files changed, 8 insertions(+), 4 deletions(-)

Comments

Philippe Mathieu-Daudé Jan. 29, 2020, 5:02 p.m. UTC | #1 
On 1/29/20 3:06 PM, Denis Plotnikov wrote:
> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>

typo VIRTQUEUE_DEFUALT_SIZE -> VIRTQUEUE_DEFAULT_SIZE in subject

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

> ---
>   hw/block/virtio-blk.c      | 6 ++++--
>   hw/scsi/virtio-scsi.c      | 5 +++--
>   include/hw/virtio/virtio.h | 1 +
>   3 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 09f46ed85f..72f935033f 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -914,7 +914,8 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
>       memset(&blkcfg, 0, sizeof(blkcfg));
>       virtio_stq_p(vdev, &blkcfg.capacity, capacity);
>       virtio_stl_p(vdev, &blkcfg.seg_max,
> -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
> +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 :
> +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
>       virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
>       virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
>       virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size);
> @@ -1272,7 +1273,8 @@ static Property virtio_blk_properties[] = {
>       DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
>                       true),
>       DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
> -    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
> +    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size,
> +                       VIRTQUEUE_DEFAULT_SIZE),
>       DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
>       DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
>                        IOThread *),
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index 3b61563609..36f66046ae 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -660,7 +660,8 @@ static void virtio_scsi_get_config(VirtIODevice *vdev,
>   
>       virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues);
>       virtio_stl_p(vdev, &scsiconf->seg_max,
> -                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2);
> +                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 :
> +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
>       virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors);
>       virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun);
>       virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
> @@ -965,7 +966,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
>   static Property virtio_scsi_properties[] = {
>       DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
>       DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
> -                                         parent_obj.conf.virtqueue_size, 128),
> +                       parent_obj.conf.virtqueue_size, VIRTQUEUE_DEFAULT_SIZE),
>       DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
>                         parent_obj.conf.seg_max_adjust, true),
>       DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index b69d517496..a66ea2368b 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -48,6 +48,7 @@ size_t virtio_feature_get_config_size(VirtIOFeature *features,
>   typedef struct VirtQueue VirtQueue;
>   
>   #define VIRTQUEUE_MAX_SIZE 1024
> +#define VIRTQUEUE_DEFAULT_SIZE 128
>   
>   typedef struct VirtQueueElement
>   {
>
Cornelia Huck Jan. 29, 2020, 5:55 p.m. UTC | #2 
On Wed, 29 Jan 2020 17:06:59 +0300
Denis Plotnikov <dplotnikov@virtuozzo.com> wrote:

> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
> ---
>  hw/block/virtio-blk.c      | 6 ++++--
>  hw/scsi/virtio-scsi.c      | 5 +++--
>  include/hw/virtio/virtio.h | 1 +
>  3 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 09f46ed85f..72f935033f 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -914,7 +914,8 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
>      memset(&blkcfg, 0, sizeof(blkcfg));
>      virtio_stq_p(vdev, &blkcfg.capacity, capacity);
>      virtio_stl_p(vdev, &blkcfg.seg_max,
> -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
> +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 :
> +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
>      virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
>      virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
>      virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size);
> @@ -1272,7 +1273,8 @@ static Property virtio_blk_properties[] = {
>      DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
>                      true),
>      DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
> -    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
> +    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size,
> +                       VIRTQUEUE_DEFAULT_SIZE),
>      DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
>      DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
>                       IOThread *),
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index 3b61563609..36f66046ae 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -660,7 +660,8 @@ static void virtio_scsi_get_config(VirtIODevice *vdev,
>  
>      virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues);
>      virtio_stl_p(vdev, &scsiconf->seg_max,
> -                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2);
> +                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 :
> +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
>      virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors);
>      virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun);
>      virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
> @@ -965,7 +966,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
>  static Property virtio_scsi_properties[] = {
>      DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
>      DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
> -                                         parent_obj.conf.virtqueue_size, 128),
> +                       parent_obj.conf.virtqueue_size, VIRTQUEUE_DEFAULT_SIZE),
>      DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
>                        parent_obj.conf.seg_max_adjust, true),
>      DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index b69d517496..a66ea2368b 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -48,6 +48,7 @@ size_t virtio_feature_get_config_size(VirtIOFeature *features,
>  typedef struct VirtQueue VirtQueue;
>  
>  #define VIRTQUEUE_MAX_SIZE 1024
> +#define VIRTQUEUE_DEFAULT_SIZE 128

Going from the header only, this looks like a value that is supposed to
be used for every virtqueue... but from the users, this is only for blk
and scsi.

I don't think adding a default for everything makes sense, even if the
same value makes sense for blk and scsi.

>  
>  typedef struct VirtQueueElement
>  {
Michael S. Tsirkin Jan. 30, 2020, 1:38 p.m. UTC | #3 
On Wed, Jan 29, 2020 at 05:06:59PM +0300, Denis Plotnikov wrote:
> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>


I'm not sure what the point is. It's more or less an accident that
these two devices share the queue size, this constance
makes no sense to me.

> ---
>  hw/block/virtio-blk.c      | 6 ++++--
>  hw/scsi/virtio-scsi.c      | 5 +++--
>  include/hw/virtio/virtio.h | 1 +
>  3 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 09f46ed85f..72f935033f 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -914,7 +914,8 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
>      memset(&blkcfg, 0, sizeof(blkcfg));
>      virtio_stq_p(vdev, &blkcfg.capacity, capacity);
>      virtio_stl_p(vdev, &blkcfg.seg_max,
> -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
> +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 :
> +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
>      virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
>      virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
>      virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size);
> @@ -1272,7 +1273,8 @@ static Property virtio_blk_properties[] = {
>      DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
>                      true),
>      DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
> -    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
> +    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size,
> +                       VIRTQUEUE_DEFAULT_SIZE),
>      DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
>      DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
>                       IOThread *),
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index 3b61563609..36f66046ae 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -660,7 +660,8 @@ static void virtio_scsi_get_config(VirtIODevice *vdev,
>  
>      virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues);
>      virtio_stl_p(vdev, &scsiconf->seg_max,
> -                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2);
> +                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 :
> +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
>      virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors);
>      virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun);
>      virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
> @@ -965,7 +966,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
>  static Property virtio_scsi_properties[] = {
>      DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
>      DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
> -                                         parent_obj.conf.virtqueue_size, 128),
> +                       parent_obj.conf.virtqueue_size, VIRTQUEUE_DEFAULT_SIZE),
>      DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
>                        parent_obj.conf.seg_max_adjust, true),
>      DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index b69d517496..a66ea2368b 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -48,6 +48,7 @@ size_t virtio_feature_get_config_size(VirtIOFeature *features,
>  typedef struct VirtQueue VirtQueue;
>  
>  #define VIRTQUEUE_MAX_SIZE 1024
> +#define VIRTQUEUE_DEFAULT_SIZE 128
>  
>  typedef struct VirtQueueElement
>  {
> -- 
> 2.17.0
Stefan Hajnoczi Jan. 30, 2020, 2:56 p.m. UTC | #4 
On Wed, Jan 29, 2020 at 06:55:18PM +0100, Cornelia Huck wrote:
> On Wed, 29 Jan 2020 17:06:59 +0300
> Denis Plotnikov <dplotnikov@virtuozzo.com> wrote:
> 
> > Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
> > ---
> >  hw/block/virtio-blk.c      | 6 ++++--
> >  hw/scsi/virtio-scsi.c      | 5 +++--
> >  include/hw/virtio/virtio.h | 1 +
> >  3 files changed, 8 insertions(+), 4 deletions(-)
> > 
> > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> > index 09f46ed85f..72f935033f 100644
> > --- a/hw/block/virtio-blk.c
> > +++ b/hw/block/virtio-blk.c
> > @@ -914,7 +914,8 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
> >      memset(&blkcfg, 0, sizeof(blkcfg));
> >      virtio_stq_p(vdev, &blkcfg.capacity, capacity);
> >      virtio_stl_p(vdev, &blkcfg.seg_max,
> > -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
> > +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 :
> > +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
> >      virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
> >      virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
> >      virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size);
> > @@ -1272,7 +1273,8 @@ static Property virtio_blk_properties[] = {
> >      DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
> >                      true),
> >      DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
> > -    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
> > +    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size,
> > +                       VIRTQUEUE_DEFAULT_SIZE),
> >      DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
> >      DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
> >                       IOThread *),
> > diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> > index 3b61563609..36f66046ae 100644
> > --- a/hw/scsi/virtio-scsi.c
> > +++ b/hw/scsi/virtio-scsi.c
> > @@ -660,7 +660,8 @@ static void virtio_scsi_get_config(VirtIODevice *vdev,
> >  
> >      virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues);
> >      virtio_stl_p(vdev, &scsiconf->seg_max,
> > -                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2);
> > +                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 :
> > +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
> >      virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors);
> >      virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun);
> >      virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
> > @@ -965,7 +966,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
> >  static Property virtio_scsi_properties[] = {
> >      DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
> >      DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
> > -                                         parent_obj.conf.virtqueue_size, 128),
> > +                       parent_obj.conf.virtqueue_size, VIRTQUEUE_DEFAULT_SIZE),
> >      DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
> >                        parent_obj.conf.seg_max_adjust, true),
> >      DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
> > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > index b69d517496..a66ea2368b 100644
> > --- a/include/hw/virtio/virtio.h
> > +++ b/include/hw/virtio/virtio.h
> > @@ -48,6 +48,7 @@ size_t virtio_feature_get_config_size(VirtIOFeature *features,
> >  typedef struct VirtQueue VirtQueue;
> >  
> >  #define VIRTQUEUE_MAX_SIZE 1024
> > +#define VIRTQUEUE_DEFAULT_SIZE 128
> 
> Going from the header only, this looks like a value that is supposed to
> be used for every virtqueue... but from the users, this is only for blk
> and scsi.
> 
> I don't think adding a default for everything makes sense, even if the
> same value makes sense for blk and scsi.

Agreed, this value is too general.  VIRTIO_BLK_VQ_DEFAULT_SIZE and
VIRTIO_SCSI_VQ_DEFAULT_SIZE would make sense to me.

Stefan
Denis Plotnikov Feb. 3, 2020, 12:15 p.m. UTC | #5 
On 30.01.2020 17:56, Stefan Hajnoczi wrote:
> On Wed, Jan 29, 2020 at 06:55:18PM +0100, Cornelia Huck wrote:
>> On Wed, 29 Jan 2020 17:06:59 +0300
>> Denis Plotnikov <dplotnikov@virtuozzo.com> wrote:
>>
>>> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
>>> ---
>>>   hw/block/virtio-blk.c      | 6 ++++--
>>>   hw/scsi/virtio-scsi.c      | 5 +++--
>>>   include/hw/virtio/virtio.h | 1 +
>>>   3 files changed, 8 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
>>> index 09f46ed85f..72f935033f 100644
>>> --- a/hw/block/virtio-blk.c
>>> +++ b/hw/block/virtio-blk.c
>>> @@ -914,7 +914,8 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
>>>       memset(&blkcfg, 0, sizeof(blkcfg));
>>>       virtio_stq_p(vdev, &blkcfg.capacity, capacity);
>>>       virtio_stl_p(vdev, &blkcfg.seg_max,
>>> -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
>>> +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 :
>>> +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
>>>       virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
>>>       virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
>>>       virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size);
>>> @@ -1272,7 +1273,8 @@ static Property virtio_blk_properties[] = {
>>>       DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
>>>                       true),
>>>       DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
>>> -    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
>>> +    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size,
>>> +                       VIRTQUEUE_DEFAULT_SIZE),
>>>       DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
>>>       DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
>>>                        IOThread *),
>>> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
>>> index 3b61563609..36f66046ae 100644
>>> --- a/hw/scsi/virtio-scsi.c
>>> +++ b/hw/scsi/virtio-scsi.c
>>> @@ -660,7 +660,8 @@ static void virtio_scsi_get_config(VirtIODevice *vdev,
>>>   
>>>       virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues);
>>>       virtio_stl_p(vdev, &scsiconf->seg_max,
>>> -                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2);
>>> +                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 :
>>> +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
>>>       virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors);
>>>       virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun);
>>>       virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
>>> @@ -965,7 +966,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
>>>   static Property virtio_scsi_properties[] = {
>>>       DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
>>>       DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
>>> -                                         parent_obj.conf.virtqueue_size, 128),
>>> +                       parent_obj.conf.virtqueue_size, VIRTQUEUE_DEFAULT_SIZE),
>>>       DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
>>>                         parent_obj.conf.seg_max_adjust, true),
>>>       DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
>>> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
>>> index b69d517496..a66ea2368b 100644
>>> --- a/include/hw/virtio/virtio.h
>>> +++ b/include/hw/virtio/virtio.h
>>> @@ -48,6 +48,7 @@ size_t virtio_feature_get_config_size(VirtIOFeature *features,
>>>   typedef struct VirtQueue VirtQueue;
>>>   
>>>   #define VIRTQUEUE_MAX_SIZE 1024
>>> +#define VIRTQUEUE_DEFAULT_SIZE 128
>> Going from the header only, this looks like a value that is supposed to
>> be used for every virtqueue... but from the users, this is only for blk
>> and scsi.
>>
>> I don't think adding a default for everything makes sense, even if the
>> same value makes sense for blk and scsi.
> Agreed, this value is too general.  VIRTIO_BLK_VQ_DEFAULT_SIZE and
> VIRTIO_SCSI_VQ_DEFAULT_SIZE would make sense to me.
>
> Stefan
agree, that would be better.
Will redo and resend the series.

Denis
Denis Plotnikov Feb. 3, 2020, 12:17 p.m. UTC | #6 
On 30.01.2020 16:38, Michael S. Tsirkin wrote:
> On Wed, Jan 29, 2020 at 05:06:59PM +0300, Denis Plotnikov wrote:
>> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
>
> I'm not sure what the point is. It's more or less an accident that
> these two devices share the queue size, this constance
> makes no sense to me.
Ok, then let's just make a separate queue length constant for each type.
(Will redo and send in the next series)
Thanks!

Denis
>
>> ---
>>   hw/block/virtio-blk.c      | 6 ++++--
>>   hw/scsi/virtio-scsi.c      | 5 +++--
>>   include/hw/virtio/virtio.h | 1 +
>>   3 files changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
>> index 09f46ed85f..72f935033f 100644
>> --- a/hw/block/virtio-blk.c
>> +++ b/hw/block/virtio-blk.c
>> @@ -914,7 +914,8 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
>>       memset(&blkcfg, 0, sizeof(blkcfg));
>>       virtio_stq_p(vdev, &blkcfg.capacity, capacity);
>>       virtio_stl_p(vdev, &blkcfg.seg_max,
>> -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
>> +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 :
>> +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
>>       virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
>>       virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
>>       virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size);
>> @@ -1272,7 +1273,8 @@ static Property virtio_blk_properties[] = {
>>       DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
>>                       true),
>>       DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
>> -    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
>> +    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size,
>> +                       VIRTQUEUE_DEFAULT_SIZE),
>>       DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
>>       DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
>>                        IOThread *),
>> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
>> index 3b61563609..36f66046ae 100644
>> --- a/hw/scsi/virtio-scsi.c
>> +++ b/hw/scsi/virtio-scsi.c
>> @@ -660,7 +660,8 @@ static void virtio_scsi_get_config(VirtIODevice *vdev,
>>   
>>       virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues);
>>       virtio_stl_p(vdev, &scsiconf->seg_max,
>> -                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2);
>> +                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 :
>> +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
>>       virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors);
>>       virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun);
>>       virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
>> @@ -965,7 +966,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
>>   static Property virtio_scsi_properties[] = {
>>       DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
>>       DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
>> -                                         parent_obj.conf.virtqueue_size, 128),
>> +                       parent_obj.conf.virtqueue_size, VIRTQUEUE_DEFAULT_SIZE),
>>       DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
>>                         parent_obj.conf.seg_max_adjust, true),
>>       DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
>> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
>> index b69d517496..a66ea2368b 100644
>> --- a/include/hw/virtio/virtio.h
>> +++ b/include/hw/virtio/virtio.h
>> @@ -48,6 +48,7 @@ size_t virtio_feature_get_config_size(VirtIOFeature *features,
>>   typedef struct VirtQueue VirtQueue;
>>   
>>   #define VIRTQUEUE_MAX_SIZE 1024
>> +#define VIRTQUEUE_DEFAULT_SIZE 128
>>   
>>   typedef struct VirtQueueElement
>>   {
>> -- 
>> 2.17.0
Michael S. Tsirkin Feb. 3, 2020, 12:51 p.m. UTC | #7 
On Mon, Feb 03, 2020 at 03:17:07PM +0300, Denis Plotnikov wrote:
> 
> 
> On 30.01.2020 16:38, Michael S. Tsirkin wrote:
> > On Wed, Jan 29, 2020 at 05:06:59PM +0300, Denis Plotnikov wrote:
> > > Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
> > 
> > I'm not sure what the point is. It's more or less an accident that
> > these two devices share the queue size, this constance
> > makes no sense to me.
> Ok, then let's just make a separate queue length constant for each type.

it's just a number, I don't think we need a constant here.
If you feel it needs documentation, add a comment!

> (Will redo and send in the next series)
> Thanks!
> 
> Denis
> > 
> > > ---
> > >   hw/block/virtio-blk.c      | 6 ++++--
> > >   hw/scsi/virtio-scsi.c      | 5 +++--
> > >   include/hw/virtio/virtio.h | 1 +
> > >   3 files changed, 8 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> > > index 09f46ed85f..72f935033f 100644
> > > --- a/hw/block/virtio-blk.c
> > > +++ b/hw/block/virtio-blk.c
> > > @@ -914,7 +914,8 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
> > >       memset(&blkcfg, 0, sizeof(blkcfg));
> > >       virtio_stq_p(vdev, &blkcfg.capacity, capacity);
> > >       virtio_stl_p(vdev, &blkcfg.seg_max,
> > > -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
> > > +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 :
> > > +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
> > >       virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
> > >       virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
> > >       virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size);
> > > @@ -1272,7 +1273,8 @@ static Property virtio_blk_properties[] = {
> > >       DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
> > >                       true),
> > >       DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
> > > -    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
> > > +    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size,
> > > +                       VIRTQUEUE_DEFAULT_SIZE),
> > >       DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
> > >       DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
> > >                        IOThread *),
> > > diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> > > index 3b61563609..36f66046ae 100644
> > > --- a/hw/scsi/virtio-scsi.c
> > > +++ b/hw/scsi/virtio-scsi.c
> > > @@ -660,7 +660,8 @@ static void virtio_scsi_get_config(VirtIODevice *vdev,
> > >       virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues);
> > >       virtio_stl_p(vdev, &scsiconf->seg_max,
> > > -                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2);
> > > +                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 :
> > > +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
> > >       virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors);
> > >       virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun);
> > >       virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
> > > @@ -965,7 +966,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
> > >   static Property virtio_scsi_properties[] = {
> > >       DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
> > >       DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
> > > -                                         parent_obj.conf.virtqueue_size, 128),
> > > +                       parent_obj.conf.virtqueue_size, VIRTQUEUE_DEFAULT_SIZE),
> > >       DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
> > >                         parent_obj.conf.seg_max_adjust, true),
> > >       DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
> > > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > > index b69d517496..a66ea2368b 100644
> > > --- a/include/hw/virtio/virtio.h
> > > +++ b/include/hw/virtio/virtio.h
> > > @@ -48,6 +48,7 @@ size_t virtio_feature_get_config_size(VirtIOFeature *features,
> > >   typedef struct VirtQueue VirtQueue;
> > >   #define VIRTQUEUE_MAX_SIZE 1024
> > > +#define VIRTQUEUE_DEFAULT_SIZE 128
> > >   typedef struct VirtQueueElement
> > >   {
> > > -- 
> > > 2.17.0
Denis Plotnikov Feb. 3, 2020, 12:56 p.m. UTC | #8 
On 03.02.2020 15:51, Michael S. Tsirkin wrote:
> On Mon, Feb 03, 2020 at 03:17:07PM +0300, Denis Plotnikov wrote:
>>
>> On 30.01.2020 16:38, Michael S. Tsirkin wrote:
>>> On Wed, Jan 29, 2020 at 05:06:59PM +0300, Denis Plotnikov wrote:
>>>> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
>>> I'm not sure what the point is. It's more or less an accident that
>>> these two devices share the queue size, this constance
>>> makes no sense to me.
>> Ok, then let's just make a separate queue length constant for each type.
> it's just a number, I don't think we need a constant here.
> If you feel it needs documentation, add a comment!
I just thought that the meaningful name for the number would be better 
for the code understanding.
Anyway, If doesn't improve anything I'll just change the number and add 
a comment what it means.

Denis
>
>> (Will redo and send in the next series)
>> Thanks!
>>
>> Denis
>>>> ---
>>>>    hw/block/virtio-blk.c      | 6 ++++--
>>>>    hw/scsi/virtio-scsi.c      | 5 +++--
>>>>    include/hw/virtio/virtio.h | 1 +
>>>>    3 files changed, 8 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
>>>> index 09f46ed85f..72f935033f 100644
>>>> --- a/hw/block/virtio-blk.c
>>>> +++ b/hw/block/virtio-blk.c
>>>> @@ -914,7 +914,8 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
>>>>        memset(&blkcfg, 0, sizeof(blkcfg));
>>>>        virtio_stq_p(vdev, &blkcfg.capacity, capacity);
>>>>        virtio_stl_p(vdev, &blkcfg.seg_max,
>>>> -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
>>>> +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 :
>>>> +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
>>>>        virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
>>>>        virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
>>>>        virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size);
>>>> @@ -1272,7 +1273,8 @@ static Property virtio_blk_properties[] = {
>>>>        DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
>>>>                        true),
>>>>        DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
>>>> -    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
>>>> +    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size,
>>>> +                       VIRTQUEUE_DEFAULT_SIZE),
>>>>        DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
>>>>        DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
>>>>                         IOThread *),
>>>> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
>>>> index 3b61563609..36f66046ae 100644
>>>> --- a/hw/scsi/virtio-scsi.c
>>>> +++ b/hw/scsi/virtio-scsi.c
>>>> @@ -660,7 +660,8 @@ static void virtio_scsi_get_config(VirtIODevice *vdev,
>>>>        virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues);
>>>>        virtio_stl_p(vdev, &scsiconf->seg_max,
>>>> -                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2);
>>>> +                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 :
>>>> +                                          VIRTQUEUE_DEFAULT_SIZE - 2);
>>>>        virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors);
>>>>        virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun);
>>>>        virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
>>>> @@ -965,7 +966,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
>>>>    static Property virtio_scsi_properties[] = {
>>>>        DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
>>>>        DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
>>>> -                                         parent_obj.conf.virtqueue_size, 128),
>>>> +                       parent_obj.conf.virtqueue_size, VIRTQUEUE_DEFAULT_SIZE),
>>>>        DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
>>>>                          parent_obj.conf.seg_max_adjust, true),
>>>>        DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
>>>> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
>>>> index b69d517496..a66ea2368b 100644
>>>> --- a/include/hw/virtio/virtio.h
>>>> +++ b/include/hw/virtio/virtio.h
>>>> @@ -48,6 +48,7 @@ size_t virtio_feature_get_config_size(VirtIOFeature *features,
>>>>    typedef struct VirtQueue VirtQueue;
>>>>    #define VIRTQUEUE_MAX_SIZE 1024
>>>> +#define VIRTQUEUE_DEFAULT_SIZE 128
>>>>    typedef struct VirtQueueElement
>>>>    {
>>>> -- 
>>>> 2.17.0
diff mbox series

Patch

diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 09f46ed85f..72f935033f 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -914,7 +914,8 @@  static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
     memset(&blkcfg, 0, sizeof(blkcfg));
     virtio_stq_p(vdev, &blkcfg.capacity, capacity);
     virtio_stl_p(vdev, &blkcfg.seg_max,
-                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
+                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 :
+                                          VIRTQUEUE_DEFAULT_SIZE - 2);
     virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
     virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
     virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size);
@@ -1272,7 +1273,8 @@  static Property virtio_blk_properties[] = {
     DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
                     true),
     DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
-    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
+    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size,
+                       VIRTQUEUE_DEFAULT_SIZE),
     DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
     DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
                      IOThread *),
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 3b61563609..36f66046ae 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -660,7 +660,8 @@  static void virtio_scsi_get_config(VirtIODevice *vdev,
 
     virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues);
     virtio_stl_p(vdev, &scsiconf->seg_max,
-                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2);
+                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 :
+                                          VIRTQUEUE_DEFAULT_SIZE - 2);
     virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors);
     virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun);
     virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
@@ -965,7 +966,7 @@  static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
 static Property virtio_scsi_properties[] = {
     DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
     DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
-                                         parent_obj.conf.virtqueue_size, 128),
+                       parent_obj.conf.virtqueue_size, VIRTQUEUE_DEFAULT_SIZE),
     DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
                       parent_obj.conf.seg_max_adjust, true),
     DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index b69d517496..a66ea2368b 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -48,6 +48,7 @@  size_t virtio_feature_get_config_size(VirtIOFeature *features,
 typedef struct VirtQueue VirtQueue;
 
 #define VIRTQUEUE_MAX_SIZE 1024
+#define VIRTQUEUE_DEFAULT_SIZE 128
 
 typedef struct VirtQueueElement
 {