Re: [Qemu-devel] [snabb-devel] Re: [PATCH v2] vhost-user: add multi queue support

[Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>]

On Mon, Apr 6, 2015 at 6:07 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Sat, Jan 24, 2015 at 02:22:29PM +0200, Nikolay Nikolaev wrote:
> > Vhost-user will implement the multiqueueu support in a similar way to what
>
> multiqueue
>
> > vhost already has - a separate thread for each queue.
> >
> > To enable the multiqueue funcionality - a new command line parameter
> > "queues" is introduced for the vhost-user netdev.
> >
> > Changes since v1:
> >  - use s->nc.info_str when bringing up/down the backend
> >
> > Signed-off-by: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>
> > ---
> >  docs/specs/vhost-user.txt |    5 +++++
> >  hw/virtio/vhost-user.c    |    6 +++++-
> >  net/vhost-user.c          |   39 +++++++++++++++++++++++++--------------
> >  qapi-schema.json          |    6 +++++-
> >  qemu-options.hx           |    5 +++--
> >  5 files changed, 43 insertions(+), 18 deletions(-)
> >
> > diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
> > index 650bb18..d7b208c 100644
> > --- a/docs/specs/vhost-user.txt
> > +++ b/docs/specs/vhost-user.txt
>
> I've been thinking that the protocol might be a useful addition
> to the virtio spec. For this, as a minimum you would have to submit this
> document as a comment to virtio TC with a proposal to include it in the
> virtio spec.
> See
> https://www.oasis-open.org/committees/comments/index.php?wg_abbrev=virtio
>
> Can you do this?

This is actually a great idea. I'll post the document to the comment's list.
Do you prefer the upstream version or this one with the MQ additions?

I believe we have to go for the feature negotiation you're proposing
and then add MQ,
reconnections etc. as negotiable features on top. So for the first
version in virtio spec
we can go with this v1.0 of the vhost-user protocol.

>
> We can take it from there, though I would encourage your
> company to join as a contributor.

We'll refrain from joining the TC for the time being, but we may
consider it in the future.

>
>
> > @@ -127,6 +127,11 @@ 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 properly calculated value.
> > +
>
> Something that's not clear from this document is what happens with control VQ.
> Can you clarify please?

Well, the control VQ is a property of the virtio net device. The
vhost-user protocol operates
at the generic virtio level. It has not defined specifics for the
different device types.

It is true that the current implementation handles the control VQ in
QEMU itself. This is
because vhost-user was modeled over the 'tap' backend which exposes
only the Rx/Tx queues to the
vhost-net kernel module.

I believe this doc should stay as generic as possible, but still we
can add a note about the
current implementation. Something like:

NOTE: the current vhost-user implementation has no virtio device
specifics. In that sense
the net device handles the cotrolq in QEMU and this it is not exposed
to the slave.

regards,
Nikolay Nikolaev

>
>
> >  Message types
> >  -------------
> >
> > 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..a0b4af2 100644
> > --- a/net/vhost-user.c
> > +++ b/net/vhost-user.c
> > @@ -122,37 +122,39 @@ static void net_vhost_user_event(void *opaque, int event)
> >      case CHR_EVENT_OPENED:
> >          vhost_user_start(s);
> >          net_vhost_link_down(s, false);
> > -        error_report("chardev \"%s\" went up\n", s->chr->label);
> > +        error_report("chardev \"%s\" went up\n", s->nc.info_str);
> >          break;
> >      case CHR_EVENT_CLOSED:
> >          net_vhost_link_down(s, true);
> >          vhost_user_stop(s);
> > -        error_report("chardev \"%s\" went down\n", s->chr->label);
> > +        error_report("chardev \"%s\" went down\n", s->nc.info_str);
> >          break;
> >      }
> >  }
> >
> >  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 e16f8eb..c2cead0 100644
> > --- a/qapi-schema.json
> > +++ b/qapi-schema.json
> > @@ -2287,12 +2287,16 @@
> >  #
> >  # @vhostforce: #optional vhost on for non-MSIX virtio guests (default: false).
> >  #
> > +# @queues: #optional number of queues to be created for multiqueue vhost-user
> > +#          (Since 2.3)
> > +#
> >  # 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 85ca3ad..b5fa61f 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -1894,13 +1894,14 @@ 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
>
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