Re: [Qemu-devel] [ RFC Patch v4 1/3] virtio-net rsc: add a new host offload(rsc) feature bit

[Jason Wang <jasowang@redhat.com>]

On 04/04/2016 03:25 AM, wexu@redhat.com wrote:
> From: Wei Xu <wexu@redhat.com>
>
> A new feature bit 'VIRTIO_NET_F_GUEST_RSC' is introduced to support WHQL
> Receive-Segment-Offload test, this feature will coalesce tcp packets in
> IPv4/6 for userspace virtio-net driver.
>
> This feature can be enabled either by 'ACK' the feature when loading
> the driver in the guest, or by sending the 'VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET'
> command to the host via control queue.
>
> Signed-off-by: Wei Xu <wexu@redhat.com>
> ---
>  hw/net/virtio-net.c                         | 29 +++++++++++++++++++++++++++--
>  include/standard-headers/linux/virtio_net.h |  1 +
>  2 files changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 5798f87..bd91a4b 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -537,6 +537,7 @@ static uint64_t virtio_net_get_features(VirtIODevice *vdev, uint64_t features,
>          virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_TSO4);
>          virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_TSO6);
>          virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_ECN);
> +        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_RSC);

Several questions here:

- I think RSC should work even without vnet_hdr?
- Need we differentiate ipv4 and ipv6 like TSO here?
- And looks like this patch should be squash to following patches.

>      }
>  
>      if (!peer_has_vnet_hdr(n) || !peer_has_ufo(n)) {
> @@ -582,7 +583,8 @@ static uint64_t virtio_net_guest_offloads_by_features(uint32_t features)
>          (1ULL << VIRTIO_NET_F_GUEST_TSO4) |
>          (1ULL << VIRTIO_NET_F_GUEST_TSO6) |
>          (1ULL << VIRTIO_NET_F_GUEST_ECN)  |
> -        (1ULL << VIRTIO_NET_F_GUEST_UFO);
> +        (1ULL << VIRTIO_NET_F_GUEST_UFO)  |
> +        (1ULL << VIRTIO_NET_F_GUEST_RSC);

Looks like this is unnecessary since we won't set peer offload based on
GUEST_RSC.

>  
>      return guest_offloads_mask & features;
>  }
> @@ -1089,7 +1091,8 @@ static int receive_filter(VirtIONet *n, const uint8_t *buf, int size)
>      return 0;
>  }
>  
> -static ssize_t virtio_net_receive(NetClientState *nc, const uint8_t *buf, size_t size)
> +static ssize_t virtio_net_do_receive(NetClientState *nc,
> +                                     const uint8_t *buf, size_t size)
>  {
>      VirtIONet *n = qemu_get_nic_opaque(nc);
>      VirtIONetQueue *q = virtio_net_get_subqueue(nc);
> @@ -1685,6 +1688,26 @@ static int virtio_net_load_device(VirtIODevice *vdev, QEMUFile *f,
>      return 0;
>  }
>  
> +
> +static ssize_t virtio_net_rsc_receive(NetClientState *nc,
> +                                      const uint8_t *buf, size_t size)
> +{
> +    return virtio_net_do_receive(nc, buf, size);
> +}
> +
> +static ssize_t virtio_net_receive(NetClientState *nc,
> +                                  const uint8_t *buf, size_t size)
> +{
> +    VirtIONet *n;
> +
> +    n = qemu_get_nic_opaque(nc);
> +    if (n->curr_guest_offloads & VIRTIO_NET_F_GUEST_RSC) {
> +        return virtio_net_rsc_receive(nc, buf, size);
> +    } else {
> +        return virtio_net_do_receive(nc, buf, size);
> +    }
> +}

The changes here looks odd since it did nothing. Like I've mentioned,
better merge the patch into following ones.

> +
>  static NetClientInfo net_virtio_info = {
>      .type = NET_CLIENT_OPTIONS_KIND_NIC,
>      .size = sizeof(NICState),
> @@ -1909,6 +1932,8 @@ static Property virtio_net_properties[] = {
>                         TX_TIMER_INTERVAL),
>      DEFINE_PROP_INT32("x-txburst", VirtIONet, net_conf.txburst, TX_BURST),
>      DEFINE_PROP_STRING("tx", VirtIONet, net_conf.tx),
> +    DEFINE_PROP_BIT("guest_rsc", VirtIONet, host_features,
> +                    VIRTIO_NET_F_GUEST_RSC, true),

Need to compat the bit for old machine type to unbreak migration I believe?

Btw, also need a patch for virtio spec.

Thanks

>      DEFINE_PROP_END_OF_LIST(),
>  };
>  
> diff --git a/include/standard-headers/linux/virtio_net.h b/include/standard-headers/linux/virtio_net.h
> index a78f33e..5b95762 100644
> --- a/include/standard-headers/linux/virtio_net.h
> +++ b/include/standard-headers/linux/virtio_net.h
> @@ -55,6 +55,7 @@
>  #define VIRTIO_NET_F_MQ	22	/* Device supports Receive Flow
>  					 * Steering */
>  #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
> +#define VIRTIO_NET_F_GUEST_RSC  24      /* Guest can coalesce tcp packets */
>  
>  #ifndef VIRTIO_NET_NO_LEGACY
>  #define VIRTIO_NET_F_GSO	6	/* Host handles pkts w/ any GSO type */