On Thu, Nov 25, 2021 at 02:05:47PM +0800, Jason Wang wrote: > When VIRTIO_NET_F_MTU feature is not negotiated, we assume a very > large max_mtu. In this case, using small packet mode is not correct > since it may breaks the networking when MTU is grater than > ETH_DATA_LEN. > > To have a quick fix, simply enable the big packet mode when > VIRTIO_NET_F_MTU is not negotiated. This will slow down dpdk hosts which disable mergeable buffers and send standard MTU sized packets. > We can do optimization on top. I don't think it works like this, increasing mtu from guest >4k never worked, we can't regress everyone's performance with a promise to maybe sometime bring it back. > Reported-by: Eli Cohen <elic@xxxxxxxxxx> > Cc: Eli Cohen <elic@xxxxxxxxxx> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> > > --- > drivers/net/virtio_net.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 7c43bfc1ce44..83ae3ef5eb11 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -3200,11 +3200,12 @@ static int virtnet_probe(struct virtio_device *vdev) > dev->mtu = mtu; > dev->max_mtu = mtu; > > - /* TODO: size buffers correctly in this case. */ > - if (dev->mtu > ETH_DATA_LEN) > - vi->big_packets = true; > } > > + /* TODO: size buffers correctly in this case. */ > + if (dev->max_mtu > ETH_DATA_LEN) > + vi->big_packets = true; > + > if (vi->any_header_sg) > dev->needed_headroom = vi->hdr_len; > > -- > 2.25.1 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
