net_device: limit rate ot tx packets

[christian+kn@wwad.de (christian+kn at wwad.de)]

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.


Thanks,
Christian