Hi! On 14:11 Sat 13 Apr , christian+kn@xxxxxxx wrote: > Hi All, > > can someone please explain me, how the kernel handles different > transfer rates of different net_devices? Or in other words: How does > the systemcall send() know, when to block? > > An example: > cat /dev/zero | pv | nc -u <someip> > will show different throughput speeds depending on the network device, > the packets are sent over (wlan0 will be slower than eth0). > > - Can someone point out the location in the linux kernel source, where > this is handled? > > - If I register a net_device. How do I signal to the upper > network layers that my driver can only accept packets at a > certain rate? I tried stopping the egress queue by calling > netif_stop_queue(), but this only has the effect that the queue > overruns. > > > I have the feeling that I'm missing out a very vital point on how the > kernel's networking subsystem works. Unfortunately, Understanding Linux > Network Internals couldn't help me out here. I think this is what causes the behaviour: 1) If the network device is congested, packets will queue up in the qdisc 2) Socket memory gets used up, semdmsg will probably sleep here: udp_sendmsg ip_make_skb __ip_append_data sock_alloc_send_skb sock_alloc_send_pskb sock_wait_for_wmem 3) When packets are sent, the socket destructor will be called and wake up the sender: sock_wfree() sk->sk_write_space(sk); (which is sock_def_write_space) It would be interesting to see what will happen if the qdisc is smaller than the socket memory... -Michi -- programing a layer 3+4 network protocol for mesh networks see http://michaelblizek.twilightparadox.com _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
