Re: [virtio-dev] Re: [PATCH v2 1/2] virtio-net: enable configurable tx queue size

[Wei Wang <wei.w.wang@intel.com>]

On 06/22/2017 10:00 PM, Michael S. Tsirkin wrote:
> On Sat, Jun 17, 2017 at 04:38:03PM +0800, Wei Wang wrote:
> > On 06/16/2017 10:31 PM, Michael S. Tsirkin wrote:
> > > On Fri, Jun 16, 2017 at 06:48:38PM +0800, Wei Wang wrote:
> > > > This patch enables the virtio-net tx queue size to be configurable
> > > > between 256 (the default queue size) and 1024 by the user when the
> > > > vhost-user backend is used.
> > > >
> > > > Currently, the maximum tx queue size for other backends is 512 due
> > > > to the following limitations:
> > > > - QEMU backend: the QEMU backend implementation in some cases may
> > > > send 1024+1 iovs to writev.
> > > > - Vhost_net backend: there are possibilities that the guest sends
> > > > a vring_desc of memory which corsses a MemoryRegion thereby
> > > > generating more than 1024 iovs in total after translattion from
> > > > guest-physical address in the backend.
> > > >
> > > > Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> > > > ---
> > > >    hw/net/virtio-net.c            | 46 ++++++++++++++++++++++++++++++++++--------
> > > >    include/hw/virtio/virtio-net.h |  1 +
> > > >    2 files changed, 39 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> > > > index 7d091c9..e1a08fd 100644
> > > > --- a/hw/net/virtio-net.c
> > > > +++ b/hw/net/virtio-net.c
> > > > @@ -33,8 +33,11 @@
> > > >    /* previously fixed value */
> > > >    #define VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE 256
> > > > +#define VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE 256
> > > > +
> > > >    /* for now, only allow larger queues; with virtio-1, guest can downsize */
> > > >    #define VIRTIO_NET_RX_QUEUE_MIN_SIZE VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE
> > > > +#define VIRTIO_NET_TX_QUEUE_MIN_SIZE VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE
> > > >    /*
> > > >     * Calculate the number of bytes up to and including the given 'field' of
> > > > @@ -1491,18 +1494,33 @@ static void virtio_net_tx_bh(void *opaque)
> > > >    static void virtio_net_add_queue(VirtIONet *n, int index)
> > > >    {
> > > >        VirtIODevice *vdev = VIRTIO_DEVICE(n);
> > > > +    NetClientState *nc = qemu_get_queue(n->nic);
> > > >        n->vqs[index].rx_vq = virtio_add_queue(vdev, n->net_conf.rx_queue_size,
> > > >                                               virtio_net_handle_rx);
> > > > +
> > > > +    /*
> > > > +     * Currently, backends other than vhost-user don't support 1024 queue
> > > > +     * size.
> > > > +     */
> > > > +    if (n->net_conf.tx_queue_size == VIRTQUEUE_MAX_SIZE &&
> > > > +        nc->peer->info->type != NET_CLIENT_DRIVER_VHOST_USER) {
> > > > +        fprintf(stderr, "warning: %s: queue size %d not supported\n",
> > > > +                __func__, n->net_conf.tx_queue_size);
> > > > +        n->net_conf.tx_queue_size = VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE;
> > > > +    }
> > > > +
> > > Also, I suspect we can get here with no peer, and above will crash.
> > > It seems ugly to do this on each virtio_net_add_queue.
> > > How about moving this to realize?
> > The code has been re-arranged to make sure nc->peer is ready before
> > it's used, but I agree that it looks better to move the above to realize().
> >
> > Best,
> > Wei
> ping
>
> The issues left are minor, let's make progress and merge this asap

OK. I'll send out the new version soon.


Best,
Wei