From 5c0919d02066c3d0eb896c33265ad90101a6a84a Mon Sep 17 00:00:00 2001 From: "Richard W.M. Jones" Date: Thu, 10 Aug 2017 17:52:55 +0100 Subject: 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 Message-Id: <20170810165255.20865-1-rjones@redhat.com> Signed-off-by: Paolo Bonzini --- hw/scsi/virtio-scsi.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'hw/scsi/virtio-scsi.c') diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c index eb63944..aca1909 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, -- cgit v1.1