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 [off-list ref] wrote:
quoted
On Thu, Nov 25, 2021 at 02:05:47PM +0800, Jason Wang wrote:
quoted
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.
quoted
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.
quoted
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?
Maybe ... it will prevent sending large packets which did work ...
I'd tread carefully here, and I don't think this kind of thing is net
material.
quoted
quoted
Reported-by: Eli Cohen <redacted>
Cc: Eli Cohen <redacted>
Signed-off-by: Jason Wang <redacted>
---
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