Enable RX interrupts

[Stephen Hemminger]

On Sun, 31 Oct 2021 22:50:40 -0700
Jack Humphries <jack at chillysky.com> wrote:

> Hi folks,
> 
> Hope all are well. I’m trying to enable interrupts in DPDK so that my network receive thread can sleep on an epoll until packets arrive. I am using the ixgbe kernel driver and igb_uio userspace driver with an Intel 82599ES 10Gbps NIC.
> 
> I'm doing roughly the following to enable the interrupts, but the epoll never indicates that packets have arrived. The thread only handles packets when the epoll times out. I don't even see interrupts arrive from the device when monitoring /proc/interrupts.
> 
> port_conf.intr_conf.rxq = 1;
> 
> ...
> 
> CHECK_EQ(rte_eth_dev_rx_intr_ctl_q(kPort, kQueue, RTE_EPOLL_PER_THREAD,
>                                    RTE_INTR_EVENT_ADD, nullptr),
>          0); 
> CHECK_EQ(rte_eth_dev_rx_intr_enable(kPort, kQueue), 0);
> 
> ...
> 
> rte_epoll_event event;
> while (true) {
>   int n = rte_epoll_wait(RTE_EPOLL_PER_THREAD, &event, /*maxevents=*/1,
>                          /*timeout=*/1000);
>   if (n == 0) {
>     // Timeout expired.
>   } else {
>     // Received RX interrupt.
>   }
> }
> 
> Given that I don't see anything coming through in /proc/interrupts, I am going to start digging through the ixgbe driver. However, I wanted to ask here first to see if my setup is missing anything obvious. I based it closely on the l3fwd-power example, though I haven't been able to get that example up and running yet since my NIC only has one port plugged in right now and the example requires two (COVID building restrictions).

If you are going to use interrupts you need to have MSI-X to get per-queue interrupts.
The igb_uio driver doesn't support this; you need to use vfio-pci in kernel to get queue interrupts.