82599EB / Interrupt Assignment Under Linux

[BMich7]

Hello:

I'm using an 82599 EB 10Gigabit controller (with X520-2 Ethernet Server Adapter) under Linux. I'm trying to understand the RX and TX IRQ assignment.

Note I am using a dual Intel Xeon X5670 system - thus 24 threads/CPUs. What I see are 24 + 1 IRQs per port.

# cat /proc/interrupts | grep p2p1

167: 13 0 30 7046 0 50 0 0 0 0 0 0 27 0 0 0 0 0 0 0 0 0 0 0 PCI-MSI-edge p2p1-TxRx-0

.

.

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190: 13 0 0 7143 0 0 0 0 0 0 0 0 0 10 0 0 0 0 0 0 0 0 0 0 PCI-MSI-edge p2p1-TxRx-23

191: 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 PCI-MSI-edge p2p1

Questions:

1. Why do the RX/TX use the same IRQ instead of one IRQ for Tx and a separate one for Rx ?

2. Do each of the 24 IRQs correspond to a different queue?

3. Given the 24 threads, I see one p2p1-TxRx IRQ for each processor. But then there is a 25th one... what is its purpose given the other 24 seem to be tied to TxRx activity?

191: 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 PCI-MSI-edge p2p1 <---- What is the purpose of this IRQ?</strong>

Thank you