From __cpu_raise_softirq() to net_rx_action()

From __cpu_raise_softirq() to net_rx_action()

[Joshua Stewart]

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).

Any help is appreciated.

Thanks,
	Josh 

Re: From __cpu_raise_softirq() to net_rx_action()

[Randy.Dunlap]

On Sun, 22 Dec 2002, Joshua Stewart wrote:

| 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).
|
| Any help is appreciated.

What are you going to do with this good info when you have it?
Something like putting it on a web page would be very good, so that
other people with similar questions can have a reference to look at.

-- 
~Randy

Re: From __cpu_raise_softirq() to net_rx_action()

[Joshua Stewart]

After I understand it all, I will not be against putting together an
explanation of the whole process and posting it back to this mailing
list, or trying to find a Linux website that will host it.  Is this type
of this suitable for the Linux Documentation Project website?

Josh

On Sun, 2002-12-22 at 16:15, Randy.Dunlap wrote:
> On Sun, 22 Dec 2002, Joshua Stewart wrote:
> 
> | 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).
> |
> | Any help is appreciated.
> 
> What are you going to do with this good info when you have it?
> Something like putting it on a web page would be very good, so that
> other people with similar questions can have a reference to look at.
> 
> -- 
> ~Randy
> 
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Re: From __cpu_raise_softirq() to net_rx_action()

[Randy.Dunlap]

On Sun, 22 Dec 2002, Joshua Stewart wrote:

| After I understand it all, I will not be against putting together an
| explanation of the whole process and posting it back to this mailing
| list, or trying to find a Linux website that will host it.  Is this type
| of this suitable for the Linux Documentation Project website?
|
| Josh

Yes, it should be fine for LDP.

Thanks,
-- 
~Randy

| On Sun, 2002-12-22 at 16:15, Randy.Dunlap wrote:
| > On Sun, 22 Dec 2002, Joshua Stewart wrote:
| >
| > | 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).
| > |
| > | Any help is appreciated.
| >
| > What are you going to do with this good info when you have it?
| > Something like putting it on a web page would be very good, so that
| > other people with similar questions can have a reference to look at.
| >
| > --
| > ~Randy

Re: From __cpu_raise_softirq() to net_rx_action()

[Arnaldo Carvalho de Melo]

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