Re: [Qemu-devel] [PATCH v2] virtio-net: allow increasing rx queue size

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Wed, 10 Aug 2016 17:47:16 +0300
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> This allows increasing the rx queue size up to 1024: unlike with tx,
> guests don't put in huge S/G lists into RX so the risk of running into
> the max 1024 limitation due to some off-by-one seems small.
> 
> It's helpful for users like OVS-DPDK which don't do any buffering on the
> host - 1K roughly matches 500 entries in tun + 256 in the current rx
> queue, which seems to work reasonably well. We could probably make do
> with ~750 entries but virtio spec limits us to powers of two.
> It might be a good idea to specify an s/g size limit in a future
> version.
> 
> It also might be possible to make the queue size smaller down the road, 64
> seems like the minimal value which will still work (as guests seem to
> assume a queue full of 1.5K buffers is enough to process the largest
> incoming packet, which is ~64K).  No one actually asked for this, and
> with virtio 1 guests can reduce ring size without need for host
> configuration, so don't bother with this for now.
> 
> Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Suggested-by: Patrik Hermansson <phermansson@gmail.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> 
> changes from v1:
>     add macros as suggested by Cornelia
> 
>  include/hw/virtio/virtio-net.h |  1 +
>  hw/net/virtio-net.c            | 26 +++++++++++++++++++++++++-
>  2 files changed, 26 insertions(+), 1 deletion(-)

Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>