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

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

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:      53849          0          0          0   xen-dyn-event     
> vif1.1-q0-tx
> 107:          1          0          0          0   xen-dyn-event     
> vif1.1-q0-rx
> 108:      61460          0          0          0   xen-dyn-event     
> vif1.1-q1-tx
> 109:          1          0          0          0   xen-dyn-event     
> vif1.1-q1-rx
> 110:      67118          0          0          0   xen-dyn-event     
> vif1.1-q2-tx
> 111:          1          0          0          0   xen-dyn-event     
> vif1.1-q2-rx
> 112:      58273          0          0          0   xen-dyn-event     
> vif1.1-q3-tx
> 113:          1          0          0          0   xen-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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