Re: [Qemu-devel] [PATCH] vhost-user: multiqueue support

["Michael S. Tsirkin" <mst@redhat.com>]

On Sat, Dec 06, 2014 at 06:52:56PM +0200, Nikolay Nikolaev wrote:
> Vhost-user will implement the multiqueueu support in a similar way to what
> vhost already has - a separate thread for each queue.
> 
> To enable multiquue funcionality - a new command line parameter
> "queues" is introduced for the vhost-user netdev.
> 
> Signed-off-by: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>

Nikolay - plan to repost addressing comments?

> ---
>  docs/specs/vhost-user.txt |    7 +++++++
>  hw/virtio/vhost-user.c    |    6 +++++-
>  net/vhost-user.c          |   35 +++++++++++++++++++++++------------
>  qapi-schema.json          |    5 ++++-
>  qemu-options.hx           |    5 +++--
>  5 files changed, 42 insertions(+), 16 deletions(-)
> 
> diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
> index 650bb18..d3857f5 100644
> --- a/docs/specs/vhost-user.txt
> +++ b/docs/specs/vhost-user.txt
> @@ -127,6 +127,13 @@ in the ancillary data:
>  If Master is unable to send the full message or receives a wrong reply it will
>  close the connection. An optional reconnection mechanism can be implemented.
>  
> +Multi queue suport
> +---------------------
> +The protocol supports multiple queues by setting all index fields in the sent
> +messages to a value calculated by the following formula:
> +<queue idx> + <vring idx>
> +The <queue idx> is increased by 2.
> +
>  Message types
>  -------------
>  

How is the support negotiated though?
What if I set queues=N with a legacy backend that
does not support multiqueue?

> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index aefe0bb..83ebcaa 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -253,17 +253,20 @@ static int vhost_user_call(struct vhost_dev *dev, unsigned long int request,
>      case VHOST_SET_VRING_NUM:
>      case VHOST_SET_VRING_BASE:
>          memcpy(&msg.state, arg, sizeof(struct vhost_vring_state));
> +        msg.state.index += dev->vq_index;
>          msg.size = sizeof(m.state);
>          break;
>  
>      case VHOST_GET_VRING_BASE:
>          memcpy(&msg.state, arg, sizeof(struct vhost_vring_state));
> +        msg.state.index += dev->vq_index;
>          msg.size = sizeof(m.state);
>          need_reply = 1;
>          break;
>  
>      case VHOST_SET_VRING_ADDR:
>          memcpy(&msg.addr, arg, sizeof(struct vhost_vring_addr));
> +        msg.addr.index += dev->vq_index;
>          msg.size = sizeof(m.addr);
>          break;
>  
> @@ -271,7 +274,7 @@ static int vhost_user_call(struct vhost_dev *dev, unsigned long int request,
>      case VHOST_SET_VRING_CALL:
>      case VHOST_SET_VRING_ERR:
>          file = arg;
> -        msg.u64 = file->index & VHOST_USER_VRING_IDX_MASK;
> +        msg.u64 = (file->index + dev->vq_index) & VHOST_USER_VRING_IDX_MASK;
>          msg.size = sizeof(m.u64);
>          if (ioeventfd_enabled() && file->fd > 0) {
>              fds[fd_num++] = file->fd;
> @@ -313,6 +316,7 @@ static int vhost_user_call(struct vhost_dev *dev, unsigned long int request,
>                  error_report("Received bad msg size.\n");
>                  return -1;
>              }
> +            msg.state.index -= dev->vq_index;
>              memcpy(arg, &msg.state, sizeof(struct vhost_vring_state));
>              break;
>          default:
> diff --git a/net/vhost-user.c b/net/vhost-user.c
> index 24e050c..1ea2f98 100644
> --- a/net/vhost-user.c
> +++ b/net/vhost-user.c
> @@ -134,25 +134,27 @@ static void net_vhost_user_event(void *opaque, int event)
>  
>  static int net_vhost_user_init(NetClientState *peer, const char *device,
>                                 const char *name, CharDriverState *chr,
> -                               bool vhostforce)
> +                               bool vhostforce, uint32_t queues)
>  {
>      NetClientState *nc;
>      VhostUserState *s;
> +    int i;
>  
> -    nc = qemu_new_net_client(&net_vhost_user_info, peer, device, name);
> +    for (i = 0; i < queues; i++) {
> +        nc = qemu_new_net_client(&net_vhost_user_info, peer, device, name);
>  
> -    snprintf(nc->info_str, sizeof(nc->info_str), "vhost-user to %s",
> -             chr->label);
> +        snprintf(nc->info_str, sizeof(nc->info_str), "vhost-user%d to %s",
> +                 i, chr->label);
>  
> -    s = DO_UPCAST(VhostUserState, nc, nc);
> +        s = DO_UPCAST(VhostUserState, nc, nc);
>  
> -    /* We don't provide a receive callback */
> -    s->nc.receive_disabled = 1;
> -    s->chr = chr;
> -    s->vhostforce = vhostforce;
> -
> -    qemu_chr_add_handlers(s->chr, NULL, NULL, net_vhost_user_event, s);
> +        /* We don't provide a receive callback */
> +        s->nc.receive_disabled = 1;
> +        s->chr = chr;
> +        s->vhostforce = vhostforce;
>  
> +        qemu_chr_add_handlers(s->chr, NULL, NULL, net_vhost_user_event, s);
> +    }
>      return 0;
>  }
>  
> @@ -228,6 +230,7 @@ static int net_vhost_check_net(QemuOpts *opts, void *opaque)
>  int net_init_vhost_user(const NetClientOptions *opts, const char *name,
>                          NetClientState *peer)
>  {
> +    uint32_t queues;
>      const NetdevVhostUserOptions *vhost_user_opts;
>      CharDriverState *chr;
>      bool vhostforce;
> @@ -254,5 +257,13 @@ int net_init_vhost_user(const NetClientOptions *opts, const char *name,
>          vhostforce = false;
>      }
>  
> -    return net_vhost_user_init(peer, "vhost_user", name, chr, vhostforce);
> +    /* number of queues for multiqueue */
> +    if (vhost_user_opts->has_queues) {
> +        queues = vhost_user_opts->queues;
> +    } else {
> +        queues = 1;
> +    }
> +
> +    return net_vhost_user_init(peer, "vhost_user", name, chr, vhostforce,
> +                               queues);
>  }
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 9ffdcf8..aa3bb6f 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -2208,12 +2208,15 @@
>  #
>  # @vhostforce: #optional vhost on for non-MSIX virtio guests (default: false).
>  #
> +# @queues: #optional number of queues to be created for multiqueue vhost-user
> +#
>  # Since 2.1
>  ##
>  { 'type': 'NetdevVhostUserOptions',
>    'data': {
>      'chardev':        'str',
> -    '*vhostforce':    'bool' } }
> +    '*vhostforce':    'bool',
> +    '*queues':        'uint32' } }
>  
>  ##
>  # @NetClientOptions
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 64af16d..23f010f 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -1893,13 +1893,14 @@ The hubport netdev lets you connect a NIC to a QEMU "vlan" instead of a single
>  netdev.  @code{-net} and @code{-device} with parameter @option{vlan} create the
>  required hub automatically.
>  
> -@item -netdev vhost-user,chardev=@var{id}[,vhostforce=on|off]
> +@item -netdev vhost-user,chardev=@var{id}[,vhostforce=on|off][,queues=n]
>  
>  Establish a vhost-user netdev, backed by a chardev @var{id}. The chardev should
>  be a unix domain socket backed one. The vhost-user uses a specifically defined
>  protocol to pass vhost ioctl replacement messages to an application on the other
>  end of the socket. On non-MSIX guests, the feature can be forced with
> -@var{vhostforce}.
> +@var{vhostforce}. Use 'queues=@var{n}' to specify the number of queues to
> +be created for multiqueue vhost-user.
>  
>  Example:
>  @example
>