Re: [IRQ] IRQ affinity not working properly?

From: Nitesh Narayan Lal
Date: Wed Apr 21 2021 - 09:32:36 EST



On 3/28/21 2:45 PM, Thomas Gleixner wrote:
> 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

<snip>

>> 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?
>
>

Jesse pointed me to this thread and apologies that it took a while for me
to respond here.

I agree it will be interesting to see with which kernel version Chris is
reproducing the issue.

Initially, I thought that this issue is the same as the one that we have
been discussing in another thread [1].

However, in that case, the smp affinity mask itself is incorrect and doesn't
follow the default smp affinity mask (with irqbalance disabled).


[1] https://lore.kernel.org/lkml/1a044a14-0884-eedb-5d30-28b4bec24b23@xxxxxxxxxx/

--
Thanks
Nitesh