Re: [Qemu-devel] [PATCH 5/7] vhost_net: move vhost_net_set_vq_index ahead at vhost_net_init

[Yuanhan Liu]

On Thu, Sep 10, 2015 at 11:14:27AM +0800, Jason Wang wrote:
> 
> 
> On 09/08/2015 03:38 PM, Yuanhan Liu wrote:
> > So that we could use the `vq_index' as well in the vhost_net_init
> > stage, which is required when adding vhost-user multiple-queue support,
> > where we need the vq_index to indicate which queue pair we are gonna
> > initiate.
> >
> > vhost-user has no multiple queue support yet, hence no queue_index set
> > before. Here is a quick set to 0 at net_vhost_user_init() stage, and it
> > will be set properly soon in the next patch.
> >
> > Signed-off-by: Yuanhan Liu <address@hidden>
> > ---
> >  hw/net/vhost_net.c | 16 +++++++---------
> >  net/vhost-user.c   |  1 +
> >  2 files changed, 8 insertions(+), 9 deletions(-)
> >
> > diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> > index f9441e9..141b557 100644
> > --- a/hw/net/vhost_net.c
> > +++ b/hw/net/vhost_net.c
> > @@ -138,6 +138,11 @@ static int vhost_net_get_fd(NetClientState *backend)
> >      }
> >  }
> >  
> > +static void vhost_net_set_vq_index(struct vhost_net *net, int vq_index)
> > +{
> > +    net->dev.vq_index = vq_index;
> > +}
> > +
> >  struct vhost_net *vhost_net_init(VhostNetOptions *options)
> >  {
> >      int r;
> > @@ -167,6 +172,8 @@ struct vhost_net *vhost_net_init(VhostNetOptions 
> > *options)
> >      }
> >      net->nc = options->net_backend;
> >  
> > +    vhost_net_set_vq_index(net, net->nc->queue_index * 2);
> > +
> 
> This breaks vhost kernel multiqueue since queue_index was not
> initialized at this time.

Right, thanks for pointing it out.

> We do this in set_netdev() instead of setting
> it in each kind of netdev.

Can we move it to net_init_tap() for setting the right queue_index
for each nc?

Or, can we call vhost_net_set_vq_index twice, one at vhost_net_init(for
vhost-user mq support), another one at vhost_net_start(for vhost kernel
mq support)?

Or, do you have better ideas?

> 
> >      net->dev.nvqs = 2;
> >      net->dev.vqs = net->vqs;
> >  
> > @@ -196,11 +203,6 @@ fail:
> >      return NULL;
> >  }
> >  
> > -static void vhost_net_set_vq_index(struct vhost_net *net, int vq_index)
> > -{
> > -    net->dev.vq_index = vq_index;
> > -}
> > -
> >  static int vhost_net_set_vnet_endian(VirtIODevice *dev, NetClientState 
> > *peer,
> >                                       bool set)
> >  {
> > @@ -325,10 +327,6 @@ int vhost_net_start(VirtIODevice *dev, NetClientState 
> > *ncs,
> >          goto err;
> >      }
> >  
> > -    for (i = 0; i < total_queues; i++) {
> > -        vhost_net_set_vq_index(get_vhost_net(ncs[i].peer), i * 2);
> > -    }
> > -
> >      r = k->set_guest_notifiers(qbus->parent, total_queues * 2, true);
> >      if (r < 0) {
> >          error_report("Error binding guest notifier: %d", -r);
> > diff --git a/net/vhost-user.c b/net/vhost-user.c
> > index 93dcecd..2d6bbe5 100644
> > --- a/net/vhost-user.c
> > +++ b/net/vhost-user.c
> > @@ -146,6 +146,7 @@ static int net_vhost_user_init(NetClientState *peer, 
> > const char *device,
> >      /* We don't provide a receive callback */
> >      s->nc.receive_disabled = 1;
> >      s->chr = chr;
> > +    nc->queue_index = 0;
> >  
> 
> Fail to understand why this is needed. It will be set to correct value
> in set_netdev().

Right, it's unnecessary.

BTW, May I ask you a quick question: why set_netdev is invoked after
tap init, while it is invoked before vhost-user init?

        --yliu
> 
> >      qemu_chr_add_handlers(s->chr, NULL, NULL, net_vhost_user_event, s);
> >