Enable RX interrupts

[Jack Humphries]

Hi Dmitry,

Thanks for the quick response! Yes, I was calling rte_eth_dev_rx_intr_enable — I just tried re-arming interrupts before each call to epoll and my initial experiment shows that fixes the issue.

You are right that l3fwd-power does the re-arming as well. If possible, it would be helpful to have a comment in that example code about the re-arming since the impression I got from quickly looking at the l3fwd-power code is that interrupts are turned off because the app wants to poll for a threshold of time before “giving up” and turning interrupts back on again. I’m happy to open a pull request to add this comment, too, if you prefer.

Thanks again for your help!
Jack

> On Nov 1, 2021, at 12:46 AM, Dmitry Kozlyuk <dmitry.kozliuk at gmail.com> wrote:
> 
> 2021-10-31 22:50 (UTC-0700), Jack Humphries:
>> 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).
>> 
>> Thanks,
>> Jack Humphries
> 
> Hi Jack,
> 
> Have you called rte_eth_dev_rx_intr_enable(port_id, queue_id)?
> 
> Not sure about ixgbe, but vmxnet3 also requires rearming interrupts with it
> on each iteration before rte_epoll_wait().
> This is what l3fwd-power does by the way (see turn_on_off_intr() function).
> 
> + ixgbe maintainer just in case.