File 0328-virtio-scsi-Add-virtqueue_size-para.patch of Package qemu.19028

From: "Richard W.M. Jones" <rjones@redhat.com>
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 <rjones@redhat.com>
Message-Id: <20170810165255.20865-1-rjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 5c0919d02066c3d0eb896c33265ad90101a6a84a)
[BR: FATE#327255]
Signed-off-by: Bruce Rogers <brogers@suse.com>
---
 hw/scsi/virtio-scsi.c           | 11 +++++------
 include/hw/virtio/virtio-scsi.h |  2 +-
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index f4eff4d81aa2a6bd624b157b1969..8e4807a6e632b6d9bc1e9bd77cc8 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -909,13 +909,10 @@ void virtio_scsi_common_realize(DeviceState *dev, Error **errp,
     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);
     }
 
     if (s->conf.iothread) {
@@ -991,6 +988,8 @@ 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,
diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
index ba2f5ce07c31ed332b3bfb59f6b3..e54b8ac00f4c23f4f33d888f9715 100644
--- a/include/hw/virtio/virtio-scsi.h
+++ b/include/hw/virtio/virtio-scsi.h
@@ -31,7 +31,6 @@
 #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
@@ -47,6 +46,7 @@ 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;
     char *vhostfd;