From: Oliver Neukum <oliver@xxxxxxxxxx>
Date: Wed, 11 May 2011 19:37:47 +0200
> How is the frequency NAPI uses to poll determined? We could abuse
> this and resubmit the rx URBs only at poll time, but this feels dirty,
> because we would still leave interrupts enabled.
It's not a frequency determined internally by the networking.
It is purely event based (meaning triggered by the device's interrupt).
Control flow is:
IRQ --> irq_handler()
my_netdevice_disable_device_irq();
napi_schedule();
--> schedule POLL soft irq
SOFTIRQ --> net_rx_action()
budget = netdev_budget;
for_each_net_device_needing_polling() {
...
weight = napi_state->weight;
...
work = n->poll(n, weight);
...
budget -= work;
...
}
That's the general idea.
Basically once you take you interrupt, and disable device interrupts,
the generic net device layer calls your ->poll() routing with a "weight"
You should not process more RX packets than this value.
If you have less than "weight" work to do, you should do a napi_complete(),
which takes you out of the polling group, and re-enable device interrupts.
So the idea is that you keep getting ->poll()'d until there is no more
RX work to do.
The "weight" argument implements fairness amongst competing, actively
polling, devices on the same CPU.
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