Re: [Qemu-devel] [PATCH] virtio-net: Make virtio queue sizes configurable

[Greg Kurz]

On Tue, 15 Mar 2016 06:50:38 +0200
"Michael S. Tsirkin" <address@hidden> wrote:

> On Fri, Nov 27, 2015 at 04:02:39PM +0100, Patrik Hermansson wrote:
> > This patch adds the option to specify virtio queue sizes. Currently the
> > queue sizes is hard coded to 256, which might not be suitable for all types
> > of applications.  
> 
> Any more data here? 256 packets seems plenty. Is there a chance
> your application does not support indirect descriptors?
> That's a better approach I think.
> 
> > This patch makes it possible to specify the queue size between
> > 256 to 1024.
> > 
> > The minimum value is chosen based on the current sizes of the virtio
> > queues. The maximum queue size is based upon VIRTQUEUE_SIZE_MAX.  
> 
> To me, this seems excessive.  For example, 1024 will break if we have to
> add a virtio net header entry (on old kernels).
> 

Hi Michael,

Can you elaborate on what/how will break ?

Thanks.

--
Greg

> > ---
> >  hw/net/virtio-net.c            | 31 ++++++++++++++++++++++++++++---
> >  include/hw/virtio/virtio-net.h |  8 +++++++-
> >  2 files changed, 35 insertions(+), 4 deletions(-)
> > 
> > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> > index a877614..c4fcb39 100644
> > --- a/hw/net/virtio-net.c
> > +++ b/hw/net/virtio-net.c
> > @@ -1326,20 +1326,40 @@ static void virtio_net_tx_bh(void *opaque)
> >      }
> >  }
> >  
> > +static void virtio_net_validate_queue_limit(uint16_t *queue_size)
> > +{
> > +    if (*queue_size > VIRTIO_QUEUE_SIZE_MAX) {
> > +        error_report("queue-size: %d, exceeds maximum allowed 
> > queue-size(%d),"
> > +                     "queue-size set to %d", *queue_size, 
> > VIRTIO_QUEUE_SIZE_MAX,
> > +                      VIRTIO_QUEUE_SIZE_MAX);
> > +        *queue_size = VIRTIO_QUEUE_SIZE_MAX;
> > +    } else if (*queue_size < VIRTIO_QUEUE_SIZE_MIN) {
> > +        error_report("queue-size: %d, below minimum allowed 
> > queue-size(%d),"
> > +                     "queue-size set to %d", *queue_size, 
> > VIRTIO_QUEUE_SIZE_MIN,
> > +                      VIRTIO_QUEUE_SIZE_MIN);
> > +        *queue_size = VIRTIO_QUEUE_SIZE_MIN;
> > +    }
> > +}
> > +
> >  static void virtio_net_add_queue(VirtIONet *n, int index)
> >  {
> >      VirtIODevice *vdev = VIRTIO_DEVICE(n);
> >  
> > -    n->vqs[index].rx_vq = virtio_add_queue(vdev, 256, 
> > virtio_net_handle_rx);
> > +    virtio_net_validate_queue_limit(&n->net_conf.rx_virtqueue_sz);
> > +    virtio_net_validate_queue_limit(&n->net_conf.tx_virtqueue_sz);
> > +    n->vqs[index].rx_vq = virtio_add_queue(vdev, 
> > n->net_conf.rx_virtqueue_sz,
> > +                                           virtio_net_handle_rx);
> >      if (n->net_conf.tx && !strcmp(n->net_conf.tx, "timer")) {
> >          n->vqs[index].tx_vq =
> > -            virtio_add_queue(vdev, 256, virtio_net_handle_tx_timer);
> > +            virtio_add_queue(vdev, n->net_conf.tx_virtqueue_sz,
> > +                             virtio_net_handle_tx_timer);
> >          n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
> >                                                virtio_net_tx_timer,
> >                                                &n->vqs[index]);
> >      } else {
> >          n->vqs[index].tx_vq =
> > -            virtio_add_queue(vdev, 256, virtio_net_handle_tx_bh);
> > +            virtio_add_queue(vdev, n->net_conf.tx_virtqueue_sz,
> > +                             virtio_net_handle_tx_bh);
> >          n->vqs[index].tx_bh = qemu_bh_new(virtio_net_tx_bh, 
> > &n->vqs[index]);
> >      }
> >  
> > @@ -1826,6 +1846,11 @@ static Property virtio_net_properties[] = {
> >      DEFINE_PROP_UINT32("x-txtimer", VirtIONet, net_conf.txtimer,
> >                         TX_TIMER_INTERVAL),
> >      DEFINE_PROP_INT32("x-txburst", VirtIONet, net_conf.txburst, TX_BURST),
> > +    DEFINE_PROP_UINT16("rx_virtqueue_sz", VirtIONet, 
> > net_conf.rx_virtqueue_sz,
> > +                       RX_VIRTQUEUE_SIZE),
> > +    DEFINE_PROP_UINT16("tx_virtqueue_sz", VirtIONet, 
> > net_conf.tx_virtqueue_sz,
> > +                       TX_VIRTQUEUE_SIZE),
> > +
> >      DEFINE_PROP_STRING("tx", VirtIONet, net_conf.tx),
> >      DEFINE_PROP_END_OF_LIST(),
> >  };
> > diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> > index f3cc25f..dbcabbf 100644
> > --- a/include/hw/virtio/virtio-net.h
> > +++ b/include/hw/virtio/virtio-net.h
> > @@ -28,13 +28,19 @@
> >   * ensures fairness in the io path.  256 conveniently matches the
> >   * length of the TX queue and shows a good balance of performance
> >   * and latency. */
> > -#define TX_BURST 256
> > +#define VIRTIO_QUEUE_SIZE_MIN 256
> > +#define VIRTIO_QUEUE_SIZE_MAX VIRTQUEUE_MAX_SIZE
> > +#define RX_VIRTQUEUE_SIZE VIRTIO_QUEUE_SIZE_MIN
> > +#define TX_VIRTQUEUE_SIZE VIRTIO_QUEUE_SIZE_MIN
> > +#define TX_BURST TX_VIRTQUEUE_SIZE
> >  
> >  typedef struct virtio_net_conf
> >  {
> >      uint32_t txtimer;
> >      int32_t txburst;
> >      char *tx;
> > +    uint16_t rx_virtqueue_sz;
> > +    uint16_t tx_virtqueue_sz;
> >  } virtio_net_conf;
> >  
> >  /* Maximum packet size we can receive from tap device: header + 64k */
> > -- 
> > 1.9.1  
>