On Thu, Sep 3, 2015 at 12:06 PM, Jintack Lim <jintack@cs.columbia.edu>
wrote:

> Hi,
>
> I was trying to set irq affinity by writing a value
> to /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.
>

I checked that setting smp_affinity works on Xen4.5, x86.
So, probably this is an ARM specific issue.


>
> Thanks,
> Jintack
>
> On Thu, Sep 3, 2015 at 11:34 AM, Ian Campbell <ian.campbell@citrix.com>
> 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:      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.
>>
>>
>