Re: [RFC PATCH] sched&net: avoid over-pulling tasks due to network interrupts

[Eric Dumazet]

On 11/8/21 1:27 AM, Peter Zijlstra wrote:
> On Mon, Nov 08, 2021 at 07:08:09AM +1300, Barry Song wrote:
>> On Sat, Nov 6, 2021 at 1:25 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>>>
>>> On Fri, Nov 05, 2021 at 06:51:36PM +0800, Barry Song wrote:
>>>> From: Barry Song <song.bao.hua@xxxxxxxxxxxxx>
>>>>
>>>> In LPC2021, both Libo Chen and Tim Chen have reported the overpull
>>>> of network interrupts[1]. For example, while running one database,
>>>> ethernet is located in numa0, numa1 might be almost idle due to
>>>> interrupts are pulling tasks to numa0 because of wake_up affine.
>>>> I have seen the same problem. One way to solve this problem is
>>>> moving to a normal wakeup in network rather than using a sync
>>>> wakeup which will be more aggressively pulling tasks in scheduler
>>>> core.
>>>>
>>>> On kunpeng920 with 4numa, ethernet is located at numa0, storage
>>>> disk is located at numa2. While using sysbench to connect this
>>>> mysql machine, I am seeing numa1 is idle though numa0,2 and 3
>>>> are quite busy.
>>>>
>>>
>>>> I am not saying this patch is exactly the right approach, But I'd
>>>> like to use this RFC to connect the people of net and scheduler,
>>>> and start the discussion in this wider range.
>>>
>>> Well the normal way would be to use multi-queue crud and/or receive
>>> packet steering to get the interrupt/wakeup back to the cpu that data
>>> came from.
>>
>> The test case has been a multi-queue ethernet and irqs are balanced
>> to NUMA0 by irqbalanced or pinned to NUMA0 where the card is located
>> by the script like:
>> #!/bin/bash
>> irq_list=(`cat /proc/interrupts | grep network_name| awk -F: '{print $1}'`)
>> cpunum=0
>> for irq in ${irq_list[@]}
>> do
>> echo $cpunum > /proc/irq/$irq/smp_affinity_list
>> echo `cat /proc/irq/$irq/smp_affinity_list`
>> (( cpunum+=1 ))
>> done
>>
>> I have heard some people are working around this issue  by pinning
>> multi-queue IRQs to multiple NUMAs which can spread interrupts and
>> avoid over-pulling tasks to one NUMA only, but lose ethernet locality?
> 
> So you're doing explicitly the wrong thing with your script above and
> then complain the scheduler follows that and destroys your data
> locality?
> 
> The network folks made RPS/RFS specifically to spread the processing of
> the packets back to the CPUs/Nodes the TX happened on to increase data
> locality. Why not use that?
> 

+1

This documentation should describe how this can be done

Documentation/networking/scaling.rst

Hopefully it is not completely outdated.