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

[Jason Wang]

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?

I try to do something like this in the past but give up since I end up 
with similar list.

It would be better to consider something more smart, probably need some 
refactor for a common parent class.

Thanks


> +};
>   const size_t hw_compat_5_0_len = G_N_ELEMENTS(hw_compat_5_0);
>   
>   GlobalProperty hw_compat_4_2[] = {