Purpose of irqbalance
vshrirama at gmail.com
Wed Sep 14 07:56:48 PDT 2016
smp_affinity for all the irqs are set to 0xf. However, i still see
that the irqs are routed only to cpu0. Is there any way of finding out
why is this the case? What could be the problem?
I think that if the affinity is set like 0x1, 0x2, 0x4... it will
work.. Wanted to find out the reason why cpu0 alone is processing all
Also, from your explanation - irq balance uses only the smp_affinity
sysfs entry for the irq balancing. Is this correct?
On Wed, Sep 14, 2016 at 8:06 PM, Neil Horman <nhorman at tuxdriver.com> wrote:
> On Wed, Sep 14, 2016 at 06:52:23PM +0530, Sriram V wrote:
>> Why is it that setting the smp_affinity alone is not sufficient for
>> irq to be routed to other cpus?
>> I tried doing that, but still the irq is only routed to cpu0.
>> In otherwords, why do we need a app to make the routing? how does
>> irqbalance app does that?
> Thats really two separate questions:
> 1) How does the irq smp_affinity setting affect irq routing
> 2) Why do we use irqbalance to handle affinity setting
> The answer to (1) is that the smp_affinity mask provides a user defined set of
> elligible cpus that can handle the corresponding irq. For instance, setting irq
> 10's smp_affinity to 3 (0x11) means that cpu 0 or cpu1 is allowed to handle irq
> 10's interrupt. The cpu which is actually selected is done by the hardware, and
> usually amounts to the lowest numbered cpu within the elligible set that isn't
> already handling an interrupt (which may explain, depending on how you set
> smp_affinity) why cpu0 is still handling the interrupt your interested in.
> The answer to (2) is convienience. Manually setting smp affinity for all irqs
> is a tedious process as well as an ongoing one (consider hotplug or sriov use
> cases). Irq balance can make adjustments to smp affinity to best balance irq
> workload according to different policies as irqs are allocated and freed.
> Hope that helps
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>> irqbalance at lists.infradead.org
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