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

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Stefan Hajnoczi (stefanha@redhat.com) 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>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@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" },
> +};
>  const size_t hw_compat_5_0_len = G_N_ELEMENTS(hw_compat_5_0);
>  
>  GlobalProperty hw_compat_4_2[] = {
> -- 
> 2.25.3
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK