softclock swis not bound to specific cpu

[Ivan Voras]

Robert Watson wrote:
> 
> On Sun, 18 Oct 2009, Taku YAMAMOTO wrote:
> 
>> I noticed that the softclock threads didn't seem to be bound to any cpu.
>>
>> I'm not sure whether it's the Right Thing (TM) to bind them to the 
>> corresponding cpus though: it might be good to give the scheduler a 
>> chance to rebalance callouts.
>>
>> I'm about to test the modification like the attached diff. Comments 
>> are welcome.
> 
> Yes, I think the intent is that they have a "soft" affinity to the CPU 
> where the lapic timer is firing, but not a hard binding, allowing them 
> to migrate if required.  It would be interesting to measure how 
> effective that soft affinity is in practice under various loads -- 
> presumably the goal would be for the softclock thread to migrate if a 
> higher (lower) priority thread is hogging the CPU.

So why are there NCPU softclock threads if the binding isn't important?