diff options
| author | Richard W.M. Jones <rjones@redhat.com> | 2017-08-10 17:52:55 +0100 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2017-09-19 14:09:11 +0200 |
| commit | 5c0919d02066c3d0eb896c33265ad90101a6a84a (patch) | |
| tree | e3d78d12f028a89a44f573e646921a74ec70dd5d /hw | |
| parent | aa406feadfc5b095ca147ec56d6187c64be015a7 (diff) | |
virtio-scsi: Add virtqueue_size parameter allowing virtqueue size to be set.
Since Linux switched to blk-mq as the default in Linux commit
5c279bd9e406 ("scsi: default to scsi-mq"), virtio-scsi LUNs consume
about 10x as much guest kernel memory.
This commit allows you to choose the virtqueue size for each
virtio-scsi-pci controller like this:
-device virtio-scsi-pci,id=scsi,virtqueue_size=16
The default is still 128 as before. Using smaller virtqueue_size
allows many more disks to be added to small memory virtual machines.
For a 1 vCPU, 500 MB, no swap VM I observed:
With scsi-mq enabled (upstream kernel): 175 disks
-"- ditto -"- virtqueue_size=64: 318 disks
-"- ditto -"- virtqueue_size=16: 775 disks
With scsi-mq disabled (kernel before 5c279bd9e406): 1755 disks
Note that to have any effect, this requires a kernel patch:
https://lkml.org/lkml/2017/8/10/689
Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Message-Id: <20170810165255.20865-1-rjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'hw')
| -rw-r--r-- | hw/scsi/virtio-scsi.c | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c index eb639442d1..aca1909a59 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 +917,8 @@ 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, |