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 <stefa...@redhat.com>
---
include/hw/virtio/virtio.h | 2 +-
hw/core/machine.c | 4 +++-
2 files changed, 4 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..a9bf76f318 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -28,7 +28,9 @@
#include "hw/mem/nvdimm.h"
#include "migration/vmstate.h"
-GlobalProperty hw_compat_5_0[] = {};
+GlobalProperty hw_compat_5_0[] = {
+ { "virtio-device", "packed", "off" },
+};
const size_t hw_compat_5_0_len = G_N_ELEMENTS(hw_compat_5_0);
GlobalProperty hw_compat_4_2[] = {
--
2.26.2
