case.
On 2017年01月04日 00:48, John Fastabend wrote:
On 17-01-02 10:14 PM, Jason Wang wrote:
On 2017年01月03日 06:30, John Fastabend wrote:
XDP programs can not consume multiple pages so we cap the MTU to
avoid this case. Virtio-net however only checks the MTU at XDP
program load and does not block MTU changes after the program
has loaded.
This patch sets/clears the max_mtu value at XDP load/unload time.
Signed-off-by: John Fastabend <john.r.fastab...@intel.com>
---
drivers/net/virtio_net.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 5deeda6..783e842 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1699,6 +1699,9 @@ static void virtnet_init_settings(struct net_device *dev)
.set_settings = virtnet_set_settings,
};
+#define MIN_MTU ETH_MIN_MTU
+#define MAX_MTU ETH_MAX_MTU
+
static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
{
unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
@@ -1748,6 +1751,9 @@ static int virtnet_xdp_set(struct net_device *dev,
struct bpf_prog *prog)
virtnet_set_queues(vi, curr_qp);
return PTR_ERR(prog);
}
+ dev->max_mtu = max_sz;
+ } else {
+ dev->max_mtu = ETH_MAX_MTU;
Or use ETH_DATA_LEN here consider we only allocate a size of GOOD_PACKET_LEN for
each small buffer?
Thanks
OK so this logic is a bit too simply. When it resets the max_mtu I guess it
needs to read the mtu via
virtio_cread16(vdev, ...)
or we may break the negotiated mtu.
Yes, this is a problem (even use ETH_MAX_MTU). We may need a method to
notify the device about the mtu in this case which is not supported by
virtio now.
As for capping it at GOOD_PACKET_LEN this has the nice benefit of avoiding any
underestimates in EWMA predictions because it appears min estimates are capped
at GOOD_PACKET_LEN via get_mergeable_buf_len().
This seems something misunderstanding here, I meant only use
GOOD_PACKET_LEN for small buffer (which does not use EWMA).
Thanks
Thanks,
John
