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SubjectRe: [IRQ] IRQ affinity not working properly?
Date
On Fri, Jan 29 2021 at 13:17, Chris Friesen wrote:
> I have a CentOS 7 linux system with 48 logical CPUs and a number of

Kernel version?

> Intel NICs running the i40e driver. It was booted with
> irqaffinity=0-1,24-25 in the kernel boot args, resulting in
> /proc/irq/default_smp_affinity showing "0000,03000003". CPUs 2-11 are
> set as "isolated" in the kernel boot args. The irqbalance daemon is not
> running.
>
> The problem I'm seeing is that /proc/interrupts shows iavf interrupts
> (associated with physical devices running the i40e driver) on other CPUs
> than the expected affinity. For example, here are some iavf interrupts
> on CPU 4 where I would not expect to see any interrupts given that "cat
> /proc/irq/<NUM>/smp_affinity_list" reports "0-1,24-25" for all these
> interrupts. (Sorry for the line wrapping.)
>
> cat /proc/interrupts | grep -e CPU -e 941: -e 942: -e 943: -e 944: -e
> 945: -e 961: -e 962: -e 963: -e 964: -e 965:
>
> CPU0 CPU1 CPU2 CPU3 CPU4 CPU5
> 941: 0 0 0 0 28490 0
> IR-PCI-MSI-edge iavf-0000:b5:03.6:mbx
> 942: 0 0 0 0 333832 0
> IR-PCI-MSI-edge iavf-net1-TxRx-0
> 943: 0 0 0 0 300842 0
> IR-PCI-MSI-edge iavf-net1-TxRx-1
> 944: 0 0 0 0 333845 0
> IR-PCI-MSI-edge iavf-net1-TxRx-2
> 945: 0 0 0 0 333822 0
> IR-PCI-MSI-edge iavf-net1-TxRx-3
> 961: 0 0 0 0 28492 0
> IR-PCI-MSI-edge iavf-0000:b5:02.7:mbx
> 962: 0 0 0 0 435608 0
> IR-PCI-MSI-edge iavf-net1-TxRx-0
> 963: 0 0 0 0 394832 0
> IR-PCI-MSI-edge iavf-net1-TxRx-1
> 964: 0 0 0 0 398414 0
> IR-PCI-MSI-edge iavf-net1-TxRx-2
> 965: 0 0 0 0 192847 0
> IR-PCI-MSI-edge iavf-net1-TxRx-3
>
> There were IRQs coming in on the "iavf-0000:b5:02.7:mbx" interrupt at
> roughly 1 per second without any traffic, while the interrupt rate on
> the "iavf-net1-TxRx-<X>" seemed to be related to traffic.
>
> Is this expected? It seems like the IRQ subsystem is not respecting the
> configured SMP affinity for the interrupt in question. I've also seen
> the same behaviour with igb interrupts.

No it's not expected. Do you see the same behaviour with a recent
mainline kernel, i.e. 5.10 or 5.11?

Thanks,

tglx

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