Re: Increased memory usage with scsi-mq

[Paolo Bonzini]

On 10/08/2017 17:40, Richard W.M. Jones wrote:
> OK this is looking a bit better now.
> 
>   With scsi-mq enabled:   175 disks
>   virtqueue_size=64:      318 disks *
>   virtqueue_size=16:      775 disks *
>   With scsi-mq disabled: 1755 disks
>                                     * = new results
> 
> I also ran the whole libguestfs test suite with virtqueue_size=16
> (with no failures shown).  As this tests many different disk I/O
> operations, it gives me some confidence that things generally work.

Yes, it looks good.  I'll grab you on IRC to discuss the commit message.

Paolo

> Do you have any other comments about the patches?  I'm not sure I know
> enough to write an intelligent commit message for the kernel patch.
> 
> Rich.

> 
> --- kernel patch ---
> 
> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
> index 9be211d68b15..d6b4ff634c0d 100644
> --- a/drivers/scsi/virtio_scsi.c
> +++ b/drivers/scsi/virtio_scsi.c
> @@ -972,6 +972,8 @@ static int virtscsi_probe(struct virtio_device *vdev)
>  	if (err)
>  		goto virtscsi_init_failed;
>  
> +	shost->can_queue = virtqueue_get_vring_size(vscsi->req_vqs[0].vq);
> +
>  	cmd_per_lun = virtscsi_config_get(vdev, cmd_per_lun) ?: 1;
>  	shost->cmd_per_lun = min_t(u32, cmd_per_lun, shost->can_queue);
>  	shost->max_sectors = virtscsi_config_get(vdev, max_sectors) ?: 0xFFFF;
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 5e1b548828e6..2d7509da9f39 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -296,7 +296,6 @@ static inline int virtqueue_add(struct virtqueue *_vq,
>  	}
>  #endif
>  
> -	BUG_ON(total_sg > vq->vring.num);
>  	BUG_ON(total_sg == 0);
>  
>  	head = vq->free_head;
> @@ -305,8 +304,10 @@ static inline int virtqueue_add(struct virtqueue *_vq,
>  	 * buffers, then go indirect. FIXME: tune this threshold */
>  	if (vq->indirect && total_sg > 1 && vq->vq.num_free)
>  		desc = alloc_indirect(_vq, total_sg, gfp);
> -	else
> +	else {
>  		desc = NULL;
> +		WARN_ON_ONCE(total_sg > vq->vring.num && !vq->indirect);
> +        }
>  
>  	if (desc) {
>  		/* Use a single buffer which doesn't continue */
> 
> --- qemu patch ---
> 
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index eb639442d1..aadd99aad1 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -867,10 +867,10 @@ void virtio_scsi_common_realize(DeviceState *dev,
>      s->sense_size = VIRTIO_SCSI_SENSE_DEFAULT_SIZE;
>      s->cdb_size = VIRTIO_SCSI_CDB_DEFAULT_SIZE;
>  
> -    s->ctrl_vq = virtio_add_queue(vdev, VIRTIO_SCSI_VQ_SIZE, ctrl);
> -    s->event_vq = virtio_add_queue(vdev, VIRTIO_SCSI_VQ_SIZE, evt);
> +    s->ctrl_vq = virtio_add_queue(vdev, s->conf.virtqueue_size, ctrl);
> +    s->event_vq = virtio_add_queue(vdev, s->conf.virtqueue_size, evt);
>      for (i = 0; i < s->conf.num_queues; i++) {
> -        s->cmd_vqs[i] = virtio_add_queue(vdev, VIRTIO_SCSI_VQ_SIZE, cmd);
> +        s->cmd_vqs[i] = virtio_add_queue(vdev, s->conf.virtqueue_size, cmd);
>      }
>  }
>  
> @@ -917,6 +917,7 @@ 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),
>      DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
>                                                    0xFFFF),
>      DEFINE_PROP_UINT32("cmd_per_lun", VirtIOSCSI, parent_obj.conf.cmd_per_lun,
> diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
> index de6ae5a9f6..e30a92d3e7 100644
> --- a/include/hw/virtio/virtio-scsi.h
> +++ b/include/hw/virtio/virtio-scsi.h
> @@ -48,6 +48,7 @@ typedef struct virtio_scsi_config VirtIOSCSIConfig;
>  
>  struct VirtIOSCSIConf {
>      uint32_t num_queues;
> +    uint32_t virtqueue_size;
>      uint32_t max_sectors;
>      uint32_t cmd_per_lun;
>  #ifdef CONFIG_VHOST_SCSI
> 
> 
>