linux-kernel - Re: [IRQ] IRQ affinity not working properly?

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Date:   Wed, 21 Apr 2021 09:31:37 -0400
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Chris Friesen <chris.friesen@...driver.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: Re: [IRQ] IRQ affinity not working properly?


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@redhat.com/

-- 
Thanks
Nitesh