Re: [Xen-devel] [Xen-users] Changing netback tx interrupts affinity on Dom0

[Jintack Lim <jintack@xxxxxxxxxxxxxxx>]

Hi,

I was trying to set irq affinity by writing a value toÂ/proc/irq/<irq>/smp_affinity,

but smp_affinity value was not changed at all.

Ian suggested to take this to the devel list.

I'm working on Xen4.5, ARMv8.

Thanks,

Jintack

On Thu, Sep 3, 2015 at 11:34 AM, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:

On Thu, 2015-09-03 at 10:59 -0400, Jintack Lim wrote:
> Hi,
>
> While I was running Apache server,
> I found that one of Dom0 vcpu is running 100% to handle irqs,
> and those irqs are set to be processed only on that specific vcpu.
>
> Referring to this document,
> http://wiki.xen.org/wiki/Network_Throughput_and_Performance_Guide
> I tried to change smp_affinity by writing a value to /proc/irq/<irq
> -no>/smp_affinity,
> however the smp_affinity value was not changed.
>
> I'm working on Xen 4.5 on ARMv8,
> and the irq is netback tx interrupt.
>
> # cat /proc/irq/106/smp_affinity
> 1
>
> # cat /proc/interrupts
> ...
> 106:Â Â Â 53849Â Â Â Â Â 0Â Â Â Â Â 0Â Â Â Â Â 0Â Âxen-dyn-event
> vif1.1-q0-tx
> 107:Â Â Â Â Â 1Â Â Â Â Â 0Â Â Â Â Â 0Â Â Â Â Â 0Â Âxen-dyn-event
> vif1.1-q0-rx
> 108:Â Â Â 61460Â Â Â Â Â 0Â Â Â Â Â 0Â Â Â Â Â 0Â Âxen-dyn-event
> vif1.1-q1-tx
> 109:Â Â Â Â Â 1Â Â Â Â Â 0Â Â Â Â Â 0Â Â Â Â Â 0Â Âxen-dyn-event
> vif1.1-q1-rx
> 110:Â Â Â 67118Â Â Â Â Â 0Â Â Â Â Â 0Â Â Â Â Â 0Â Âxen-dyn-event
> vif1.1-q2-tx
> 111:Â Â Â Â Â 1Â Â Â Â Â 0Â Â Â Â Â 0Â Â Â Â Â 0Â Âxen-dyn-event
> vif1.1-q2-rx
> 112:Â Â Â 58273Â Â Â Â Â 0Â Â Â Â Â 0Â Â Â Â Â 0Â Âxen-dyn-event
> vif1.1-q3-tx
> 113:Â Â Â Â Â 1Â Â Â Â Â 0Â Â Â Â Â 0Â Â Â Â Â 0Â Âxen-dyn-event
> vif1.1-q3-rx
> ...
>
> What would be the way to change smp_affinity?

It should be via /proc/irq/<irq>/smp_affinity as you've tried, I asked
Stefano and he things this was already implemented in 4.5 even. That it is
not happening would be a bug, I think.

I'd suggest you take this to the devel list as a bug.

> and where is the affinity set initially for netback tx interrupts?

Not, sure, I think it might just be generic IRQ code.

Ian.

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