Re: Increased memory usage with scsi-mq

Paolo Bonzini
2017-08-10T16:04:30Z

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
>
>
>