I would like to know if it is possible to prioritize the Ethernet
traffic till it reaches napi_gro_receive() or netif_receive_skb() called
inside the network card driver.
First I thought it is possible by the prioritization of the irq/XX-ethX
thread which is used by the network card and the NET_RX_SOFTIRQ,
NET_TX_SOFTIRQ threads. Till I read that the split from software
interrupts to threads are gone in the RT patch. Now I'm a bit confused
and unsure about the softirq handling.
I used ftrace to determine the path of an incoming packet and it looks
to me that the softirq is prozessed inside the irq/18-eth1 thread. So if
I give the irq/18-eth1 a higher priority than the others, can I be sure
that it gets not interrupted?
here a part from my ftrace:
irq/18-eth1-1738 [001] 1366.914708: function:
e1000_intr <-- irq_forced_thread_fn
irq/18-eth1-1738 [001] 1366.914711: function:
__napi_schedule <-- e1000_intr
[...]
irq/18-eth1-1738 [001] 1366.914718: function:
__do_softirq <-- local_bh_enable
irq/18-eth1-1738 [001] 1366.914719: function:
__do_softirq_common <-- __do_softirq
irq/18-eth1-1738 [001] 1366.914719: function:
net_rx_action <-- __do_softirq_common
irq/18-eth1-1738 [001] 1366.914720: function:
e1000_clean <-- net_rx_action
irq/18-eth1-1738 [001] 1366.914721: function:
e1000_clean_rx_irq <-- e1000_clean
irq/18-eth1-1738 [001] 1366.914722: function:
__netdev_alloc_skb <-- e1000_clean_rx_irq
irq/18-eth1-1738 [001] 1366.914722: function:
__alloc_skb <-- __netdev_alloc_skb
[...]
irq/18-eth1-1738 [001] 1366.914744: function:
e1000_receive_skb <-- e1000_clean_rx_irq
irq/18-eth1-1738 [001] 1366.914744: function:
eth_type_trans <-- e1000_receive_skb
irq/18-eth1-1738 [001] 1366.914744: function:
napi_gro_receive <-- e1000_receive_skb
I hope someone can explain it to me. The reason I want to prioritize the
incoming network traffic is cause I'm writing a module for the
TTEthernet protocol which is Time-triggered and and based on the
standard Ethernet. I need the packets without or very less jitter. And I
would like to use it by changing the napi_gro_receive() funtion in the
network card driver to my module function to use it with any card by
almost no modification in the code.
I'm quite new to kernel development and the module I'm writing is part
of my bachelor thesis. If there is a paper or a book who explains this
behavior I'm happy to know about it!
Best regards
Frieder
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