On Wed, Dec 01, 2021 at 08:15:28PM +0000, Pavel Begunkov wrote: > On 12/1/21 19:20, David Ahern wrote: > > On 12/1/21 12:11 PM, Pavel Begunkov wrote: > > > btw, why a dummy device would ever go through loopback? It doesn't > > > seem to make sense, though may be missing something. > > > > You are sending to a local ip address, so the fib_lookup returns > > RTN_LOCAL. The code makes dev_out the loopback: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tree/net/ipv4/route.c#n2773 > > I see, thanks. I still don't use the skb_orphan_frags_rx() hack > and it doesn't go through the loopback (for my dummy tests), just > dummy_xmit() and no mention of loopback in perf data, see the > flamegraph. Don't know what is the catch. > > I'm illiterate of the routing paths. Can it be related to > the "ip route add"? How do you get an ipv4 address for the device? I also bumped into the udp-connect() => ECONNREFUSED (111) error from send-zc. because I assumed no server is needed by using dummy. Then realized the cover letter mentioned msg_zerocopy is used as the server. Mentioning just in case someone hits it also. To tx out dummy, I did: #> ip a add 10.0.0.1/24 dev dummy0 #> ip -4 r 10.0.0.0/24 dev dummy0 proto kernel scope link src 10.0.0.1 #> ./send-zc -4 -D 10.0.0.(2) -t 10 udp ip -s link show dev dummy0 2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 65535 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000 link/ether 82:0f:e0:dc:f7:e6 brd ff:ff:ff:ff:ff:ff RX: bytes packets errors dropped missed mcast 0 0 0 0 0 0 TX: bytes packets errors dropped carrier collsns 140800890299 2150397 0 0 0 0
