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SubjectRe: [PATCH] x86: Add check for number of available vectors before CPU down [v2]


On 12/19/2013 01:05 PM, Tony Luck wrote:
> On Wed, Dec 18, 2013 at 11:50 AM, Tony Luck <tony.luck@intel.com> wrote:
>> Looks good to me.
>
> Though now I've been confused by an offline question about affinity.

Heh :) I'm pursuing it now. Rui has asked a pretty good question that I don't
know the answer to off the top of my head. I'm still looking at the code.

>
> Suppose we have some interrupt that has affinity to multiple cpus. E.g.
> (real example from one of my machines):
>
> # cat /proc/irq/94/smp_affinity_list
> 26,54
>
> Now If I want to take either cpu26 or cpu54 offline - I'm guessing that I don't
> really need to find a new home for vector 94 - because the other one of that
> pair already has that set up. But your check_vectors code doesn't look like
> it accounts for that - if we take cpu26 offline - it would see that
> cpu54 doesn't
> have 94 free - but doesn't check that it is for the same interrupt.
>
> But I may be mixing "vectors" and "irqs" here.

Yep. The question really is this: is the irq mapped to a single vector or
multiple vectors. (I think)

P.

>
> -Tony


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