On Thu, Nov 25, 2021 at 03:20:07PM +0800, Jason Wang wrote: > On Thu, Nov 25, 2021 at 3:15 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > > On Thu, Nov 25, 2021 at 03:11:58PM +0800, Jason Wang wrote: > > > On Thu, Nov 25, 2021 at 3:00 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > > > > > > 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, > > > > > > Looking at add_recvbuf_small() it's actually GOOD_PACKET_LEN if I was not wrong. > > > > OK, even more so then. > > > > > > we can't regress everyone's > > > > performance with a promise to maybe sometime bring it back. > > > > > > So consider it never work before I wonder if we can assume a 1500 as > > > max_mtu value instead of simply using MAX_MTU? > > > > > > Thanks > > > > You want to block guests from setting MTU to a value >GOOD_PACKET_LEN? > > Yes, or fix the issue to let large packets on RX work (e.g as the TODO > said, size the buffer: for <=4K mtu continue to work as > add_recvbuf_small(), for >= 4K switch to use big). Right. The difficulty is with changing modes, current code isn't designed for it. > > Maybe ... it will prevent sending large packets which did work ... > > Yes, but it's strange to allow TX but not RX > > > I'd tread carefully here, and I don't think this kind of thing is net > > material. > > I agree consider it can't be fixed easily. > > Thanks > > > > > > > > > > > > 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
