Re: From __cpu_raise_softirq() to net_rx_action()

[Arnaldo Carvalho de Melo <acme@conectiva.com.br>]

Em Sun, Dec 22, 2002 at 04:11:37PM -0500, Joshua Stewart escreveu:
> I'm still trying to follow a packet (or even better an sk_buff) from the
> NIC card to user space.  I think I have a good chunk of it figured out,
> but I'm missing a bit from the time that the __netif_rx_schedule()
> routine calls __cpu_raise_softirq() until the routine net_rx_action()
> occurs.  I read in a book on Linux TCP/IP implementation that the
> softirq basically leads to a call to net_rx_action(), but I don't see
> the connection yet.  It's probably due to my lack of understanding of
> IRQ's (and software IRQ's).

You need to read about softirqs, but here is a quick explanation: there are
several points where softirqs are serviced, like bottom halves were in the
past (softirqs are much nicer), one example:

do_IRQ -> irq_exit -> do_softirq -> net_rx_action

So basically search for places calling do_softirq, they look if there is
softirqs pending and call do_softirq that will call the appropriate _action
function registered at softirq creation (look at net/core/dev.c, function
net_dev_init, line 2875.

- Arnaldo