On Fri, May 29, 2020 at 03:15:59PM +0800, Jason Wang wrote:
> 
> On 2020/5/23 上午1:17, Stefan Hajnoczi wrote:
> > 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 <stefanha@redhat.com>
> > ---
> >   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" },
> 
> 
> Missing "vhost-user-gpu" here?

Thanks, you're right.

I'll see if virtio-gpu-base works. If not it will be necessary to add
all the derived classes. The same is true for virtio-scsi-common, I'd
better check it works correctly!

Stefan