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 /include | |
| 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 'include')
| -rw-r--r-- | include/hw/virtio/virtio-scsi.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h index de6ae5a9f6..4c0bcdb788 100644 --- a/include/hw/virtio/virtio-scsi.h +++ b/include/hw/virtio/virtio-scsi.h @@ -32,7 +32,6 @@ #define VIRTIO_SCSI(obj) \ OBJECT_CHECK(VirtIOSCSI, (obj), TYPE_VIRTIO_SCSI) -#define VIRTIO_SCSI_VQ_SIZE 128 #define VIRTIO_SCSI_MAX_CHANNEL 0 #define VIRTIO_SCSI_MAX_TARGET 255 #define VIRTIO_SCSI_MAX_LUN 16383 @@ -48,6 +47,7 @@ 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 |