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

[Prarit Bhargava <prarit@redhat.com>]

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