[PATCH 5/5] virtio: enable VIRTIO_F_RING_PACKED for all devices

[Stefan Hajnoczi]

The packed virtqueue layout was introduced in VIRTIO 1.1. It is a single
ring instead of a split avail/used ring design. There are CPU cache
advantages to this layout and it is also suited better to hardware
implementation.

The vhost-net backend has already supported packed virtqueues for some
time. Performance benchmarks show that virtio-blk performance on NVMe
drives is also improved.

Go ahead and enable this feature for all VIRTIO devices. Keep it
disabled for QEMU 5.0 and earlier machine types.

Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 include/hw/virtio/virtio.h |  2 +-
 hw/core/machine.c          | 18 +++++++++++++++++-
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index b69d517496..fd5b4a2044 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -292,7 +292,7 @@ typedef struct VirtIORNGConf VirtIORNGConf;
     DEFINE_PROP_BIT64("iommu_platform", _state, _field, \
                       VIRTIO_F_IOMMU_PLATFORM, false), \
     DEFINE_PROP_BIT64("packed", _state, _field, \
-                      VIRTIO_F_RING_PACKED, false)
+                      VIRTIO_F_RING_PACKED, true)
 
 hwaddr virtio_queue_get_desc_addr(VirtIODevice *vdev, int n);
 bool virtio_queue_enabled(VirtIODevice *vdev, int n);
diff --git a/hw/core/machine.c b/hw/core/machine.c
index bb3a7b18b1..3598c3c825 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -28,7 +28,23 @@
 #include "hw/mem/nvdimm.h"
 #include "migration/vmstate.h"
 
-GlobalProperty hw_compat_5_0[] = {};
+GlobalProperty hw_compat_5_0[] = {
+    { "vhost-user-blk", "packed", "off" },
+    { "vhost-user-fs-device", "packed", "off" },
+    { "vhost-vsock-device", "packed", "off" },
+    { "virtio-9p-device", "packed", "off" },
+    { "virtio-balloon-device", "packed", "off" },
+    { "virtio-blk-device", "packed", "off" },
+    { "virtio-crypto-device", "packed", "off" },
+    { "virtio-gpu-device", "packed", "off" },
+    { "virtio-input-device", "packed", "off" },
+    { "virtio-iommu-device", "packed", "off" },
+    { "virtio-net-device", "packed", "off" },
+    { "virtio-pmem", "packed", "off" },
+    { "virtio-rng-device", "packed", "off" },
+    { "virtio-scsi-common", "packed", "off" },
+    { "virtio-serial-device", "packed", "off" },
+};
 const size_t hw_compat_5_0_len = G_N_ELEMENTS(hw_compat_5_0);
 
 GlobalProperty hw_compat_4_2[] = {
-- 
2.25.3